No. 69·中文精读

英伟达CTO卡根:摩尔定律快停了,算力还能一年涨10倍

Nvidia CTO Michael Kagan: Scaling Beyond Moore's Law to Million-GPU Clusters

Mellanox 联合创始人、英伟达 CTO 拆解从单卡到十万卡再到百万卡集群的网络瓶颈与架构挑战。

节目音频00:00 / 41:31
中文精读由 AI 基于原始访谈改写,非官方翻译,可能存在偏差或错误;表述以原节目为准。

2019年3月,英伟达以70亿美元收购以色列网络公司Mellanox。那一年,英伟达市值大约1000亿美元。

六年过去,市值4.5万亿美元,涨了45倍,现在是全球市值第一的公司。主持人Pat Grady开场就提到,红杉合伙人Shaun Maguire每隔半年就要论证一次:没有Mellanox,就没有今天的英伟达。

Mellanox联合创始人、现任英伟达CTO的迈克尔·卡根(Michael Kagan)在红杉播客Training Data里回忆,合并完成后他见到黄仁勋,拍胸脯说,一加一会等于十。

「我低估了四倍。」

卡根在半导体行业干了四十多年:先在英特尔做16年,做到首席架构师;25年前联合创办Mellanox;2019年之后,负责定义英伟达的技术方向。这期节目覆盖了从NVLink、BlueField DPU到液冷、气候模拟器的完整版图,核心就一句话:单芯片的摩尔定律快到头了,算力增长换了一条路,把几十万颗芯片连成一台机器来用。

摩尔定律两年翻倍,AI要一年10倍

卡根先给了一组对比。传统硅工艺的摩尔定律,性能每两年翻一倍。AI进场之后,模型规模每三个月翻一倍,换算下来,算力需求一年要涨10倍到16倍。

「旧学派是两年翻一倍,现在是一年10倍。」

转折点在2010年、2011年前后。GPU从「图形处理器」变成「通用处理器」,AI工作负载第一次跑上GPU,吃的是它的可编程性和并行能力。从那时起,性能需求的增长系数彻底变了。

麻烦在于,往单颗芯片里塞更多晶体管这条路,物理上已经快走不通了。卡根的原话是,摩尔定律在物理层面「不太跑得动了」。要继续喂饱指数曲线,创新得发生在比单个元件更大的尺度上。

那个更大的尺度,就是网络。红杉在节目介绍里把这件事说得很直白:AI竞赛归根结底是硅的竞赛,比的是从每一单位硅里榨出多少智能。过去是把晶体管往一颗芯片里塞,现在是把成千上万颗芯片连成一张统一的计算网络,铺满整个数据中心。卡根补了一句:性能扩展有很多层,每一层都需要高速、高性能的网络。

一块要叉车才搬得动的「GPU」

卡根把算力扩展分成两层。

第一层叫scale up,纵向扩展,把单个计算单元做大。CPU时代的纵向扩展是加晶体管、乱序执行、上多核。GPU时代的答案是NVLink。今天下单买一颗「GPU」,送到家的是一整个机柜。主持人接了一句:大家以为买的是芯片,其实买的是一套系统。卡根的原话更传神:

今天的GPU是一台石头那么大的机器,你得用叉车才搬得动。所以在亚马逊上买GPU的人,别奇怪,送来的是一大排机架。

NVLink把72颗GPU连在一起,对外呈现成一颗GPU。这72颗其实是36台计算机,每台装两颗GPU,用线缆织成一台机器。关键在软件:从1颗到72颗,接口不变,CUDA还是那套CUDA,应用感知不到下面拆成了多少块。卡根提醒,这个故事他讲得简化了,但方向准确:硬件、线缆、网络,加上把这一切暴露成CUDA API的软件层,合起来才是今天这颗「GPU」。

第二层叫scale out,横向扩展。纵向扩展做到功耗、成本、效率允许的极限,就把很多个这样的积木块连起来,在应用层面把任务拆成多份并行跑。纵向扩展的本质,是把「内存域」扩大到单颗GPU之外。收购Mellanox之前,NVLink的纵向扩展被锁在单个机柜里,跨出单节点要靠大量软件和网络技术,让多个机柜协同成一台机器。这一块,Mellanox补上了。

峰值带宽是虚的,抖动才是命门

把一个任务拆成1000份,分给1000颗GPU,1秒的活1毫秒干完。听起来很美,但拆完之后要通信:分发子任务,汇总结果,每一轮迭代里通信和计算交替出现。

调优过的应用,会把通信藏在计算背后。通信一旦变慢,所有人都在等,整台机器被最慢的那次通信拖住。所以网络的关键指标,除了峰值带宽,还有延迟分布要足够窄。

卡根说,把一个比特从A送到B,这是物理问题,各家方案的峰值数字差距不大,「我们稍微好一点,但这不算大优势」。差距在重复几千次之后显形:英伟达的网络每次耗时几乎一样,别家方案的耗时会散开一大片。

散开的代价很直接:为了给网络抖动留余量,本来能拆给1000颗GPU的任务,只能拆给10颗。网络的抖动,直接决定集群的性能上限。

所以英伟达看数据中心的眼光变了:10万颗GPU加整套网络,就是一台计算机,架构、软件、硬件全按这个粒度设计。一台这样的机器要重新设计多颗计算芯片和多颗网络芯片,投入量级可想而知。

网络还有面向客户的那一面。数据中心要跑操作系统、服务多个租户,这是BlueField DPU的活。传统计算机里,CPU既要跑应用,又要跑操作系统和网络栈,两件事抢同一颗芯片的时间。一台机器的效率,取决于通用算力里有多少真正花在应用上。BlueField把基础设施计算搬到独立的计算平台上,应用吃满通用算力,安全边界也清晰了。卡根提了差不多十年前的Meltdown侧信道攻击,基础设施和应用挤在同一个CPU上,这类攻击就防不住;分开跑,攻击面大幅缩小。

顺带一个数据:卡根说,英伟达现在的以太网业务是「有史以来增长最快的以太网业务」,这还没算NVLink和InfiniBand。

十万卡之后:坏是常态,光速是天花板

Pat Grady问,往10万卡甚至100万卡走,什么东西会先坏?卡根给了两道坎。

第一道是故障率。单个硬件组件的可用性可以做到99.999%以上,一台机器装几个组件,没问题。可10万卡的机器,折算成组件是几百万个,所有组件同时正常的概率是零。一定有东西是坏的,硬件和软件都得按「带病运行」设计,还得尽量保住性能和能效。很多工程师设计机器时默认「组件是好的,跑起来再调」,这个直觉在几万卡尺度就失效了。

第二道是光速。工作负载要跨数据中心部署,机房之间可能隔几十公里,甚至跨大陆,不同位置的延迟差异变得巨大,拥塞管理跟着变难。拆分的需求很现实:算力太大,一个园区放不下,电力也不允许。

老电信时代的办法,是在数据中心边缘放一个大缓冲区当减震器。卡根明确反对:「大缓冲区不好,越大越好是错觉,缓冲区本身就是抖动的来源。」跨机房跑同一个任务,每一台机器都得知道自己发出的通信是长是短,动态调整发送模式,从源头避开拥塞。英伟达为此做了Spectrum-X交换机,放在数据中心边缘,把遥测信息喂给端点,让端点自己调。

Pat追问,这是训练特有的问题吗?卡根说,什么都一样,只看规模。他补了一个细节:有时候整个数据中心只跑一个任务,软硬件要一起提供接口,把任务的不同部分摆到最合适的位置。这种网络跟通用数据中心网络完全是两码事。通用网络服务的是松耦合的微服务,各干各的;这里是10万台机器协同跑同一个应用。

推理比训练更吃算力,很多人还没转过来

主持人Sonya Huang问,需求是不是正从预训练转向推理。卡根的回答更进一步:推理的算力需求已经追上甚至超过训练,而且差距会继续拉大。

先看训练。卡根拆了训练的三个阶段:前向传播,本质是一次推理;反向传播,调整权重;数据并行训练还要在多份模型副本之间汇总权重更新。直到不久前,训练都是算力的绝对主力。

推理这边,卡根梳理了三次进化。最早是感知式AI,看一张图,说「这是狗」,一次推理结束。然后是生成式AI,每输出一个token,整台机器从头再跑一遍,一篇回答就是几十上百次推理。现在是推理模型,问它一个复杂问题,它要比较多条解题路径,每条路径都是推理。

推理内部还分两段:prefill处理提示词、建立上下文,吃算力;decode一个token一个token往外蹦,吃显存带宽。

为什么推理总量会超过训练?卡根给了两个理由。一是单次推理的算力消耗比感知时代涨了几个量级。二是那笔最简单的账:模型只训练一次,推理却要做亿万次。ChatGPT训练一次,几亿用户天天轰它,现在还加上了视频生成。

这里他抖了个包袱:「我妻子发现ChatGPT之后,现在跟它聊天的时间比跟我多,那是她最好的朋友。」

机器形态上,卡根的判断是推理会分层:手机上跑小模型,数据中心跑大的。而在数据中心尺度,可编程性比硬件定制更划算。每一种定制硬件都有自己的成本和代价,负载一变就闲置。英伟达已经推出了针对prefill优化的GPU型号,但decode的卡也能干prefill的活,负载结构变了可以互相补位,接口始终是CUDA那一套。卡根说得很直白:正是这套统一接口,成就了收购Mellanox之前的英伟达。

数据中心的极限:电、热、混凝土

Pat Grady问了个好问题:芯片密度撞上量子力学,机柜撞上功耗,数据中心有没有类似的定律,大到一定程度会被通信开销压垮?

卡根的回答很实在:实际的限制是给定体积内能喂进多少电。电进来了,热还得出去。英伟达已经整体转向液冷,原因就一个:风冷撑不住现在的计算密度。

他给了一组数字:xAI那种规模的机房是100到150兆瓦,现在大家谈的是吉瓦级,已经有人在谈10吉瓦。部署速度的瓶颈是什么?卡根的原话:「取决于混凝土多久凝固。」

聊到英特尔合作(卡根在英特尔干过16年,做到首席架构师),他的框架是:冯·诺依曼机没有消失,但AI这类问题没法靠「给机器解释步骤」来解决。「我能解释很多事,但我没法解释怎么区分猫和狗。」所以方向是把加速计算融进通用计算,x86仍是主力架构。这笔合作对双方的现实意义,卡根说得直白:给英伟达和英特尔都打开了新的市场通道,去服务之前够不着的客户。

这段话里他顺带交代了英伟达的文化底色:

我们的成功,等于客户的成功,等于生态的成功,不靠竞争对手的失败。我们追求的,是给大家烤一张更大的饼。

合并的成色还有一组数字可以验证。Mellanox的另一位创始人Eyal Waldman在收购后几个月就离开了,卡根是唯一留下的创始人。他回忆,收购初期满脑子就一件事,洗澡的时候都在想:怎么让这次收购成功。英伟达为他参与创办的公司付了70亿美元,百感交集,但事已至此,任务就是让它成。结果:85%到90%的以色列老员工留了下来,英伟达在以色列的人数涨了一倍多,现在还要建新园区。卡根说,这桩交易被外界普遍看作科技史上最成功的收购,「回头看,这一步走对了」。

一年10倍,还能跑多久

Sonya把问题挑明了:黄仁勋定律是两年翻一倍,加上卡根之后,斜率是多少?她管这个叫「黄仁勋定律加卡根定律」。

卡根:「一年10倍,或者每年几个数量级。」作为参照,摩尔定律折算到一年大约是1.4倍。

支撑这个斜率的动作已经做了两三年:产品节奏从两年一代改成一年一代,每一代性能高一个数量级,而且衡量标准是整台机器的性能,单芯片跑分不算数。

能维持多久?卡根的答案很诚实:「我不知道。但我们会尽全力维持,说不定还要加速。这一切都关于指数。」他提醒,看摩尔定律曲线别用对数坐标,对数坐标把爆炸画成了直线。真实的曲线是这样的:轰一下,一年后,再轰一下。

没人预测得到下一站长什么样。他举了iPhone的例子:2007年第一代iPhone发布,谁能想到17年后,这台机器上用得最少的功能是打电话,剩下的全是电商、短信、新闻、邮件,身份认证也住在里面。卡根的结论是:「我们在做的,是给下一波创新搭平台。」

科幻的部分,卡根想的是让历史变成实验科学。物理可以做实验,历史的时间箭头只有一个方向,但如果有一个足够好的世界模拟器,比如英伟达的Earth 2气候模拟器,就能模拟今天的决策在50年后对全球变暖的影响。再往后,AI擅长观察、归纳、泛化,物理定律本身就是从现象里归纳出来的,「AI能教我们一些我们现在想象不到的物理定律」。

采访结尾,Sonya请他展望AI的未来。卡根接了乔布斯的那个比喻:计算机是「心智的自行车」。

「AI大概是一艘飞船。」

他的账是这么算的:很多事情想做,但时间和资源不够。有了AI,一个人可能干出十倍的活,而想干的事,会变成今天的一百倍。给任何一个项目负责人两倍效率的资源,他会干出四倍的活,然后想要十倍的资源,没人会说「我的人手够了」。电就是这样改变世界的,伦敦街头至今留着煤气灯的底座,当年没人想到电会让整个世界离了它转不动。

「AI也一样。新世界。」

听完这期,有几件事明天就能用:

  • 选算力基础设施,别只盯峰值带宽数字,追问延迟分布和抖动。长尾决定任务实际能拆多细,也就是集群的真实上限。
  • 做AI产品的成本模型,把推理当主变量。训练是一次性投入,推理是持续支出,prefill和decode的资源画像完全不同,规划容量时分开算。
  • 写代码别过度绑定某一代硬件。硬件一年换一代,稳定的软件接口才有复利,这是英伟达自己验证过的路径。
  • 系统设计默认故障常在。规模上去之后,所有组件同时正常的概率是零,恢复和降级能力要写进架构,别当成异常处理。
  • 评估算力需求时用指数视角做预案。两年翻一倍的直觉,会系统性低估未来三年的成本曲线。
文稿来源:sequoiacap.com;机器转写可能有识别错误,人名与数字请以音频为准。
id="podcast-transcript" data-framer-component-type="RichTextContainer" style="transform:none">IntroductionMichael Kagan: One of the interesting things about Nvidia is the culture of win-win, okay? We are not after taking a bigger piece of the existing pie. We are after baking a bigger pie for everybody, and the success—our success is our customer’s success. Our success is not the failure of our competition. Our success is success of our customers and success of the ecosystem. And I think fusing together conventional computing, von Neumann machines and accelerated computing that are provided with Nvidia, it’s probably opened yet another dimension that I’m not sure what it is, but it basically gives—you know, on the practical short-term view is it gives Nvidia and Intel channels to the market, or expanding the market and serving the markets that otherwise was more challenging. Sonya Huang:  We are delighted to hear today from one of the legends of the semiconductor industry, Michael Kagan, the CTO of Nvidia. Michael was formerly Chief Architect at Intel and later co-founder and CTO of Mellanox, which Nvidia acquired for $7 billion in March 2019. Since then, Michael has been a major driver of Nvidia’s dominance as the AI compute platform—thanks in large part to Mellanox’s interconnect technology, which has been key to pushing chips beyond Moore’s Law. The AI race is ultimately a silicon race—to squeeze the most intelligence possible out of each unit of silicon. Michael takes us on a journey through how the compute frontier has evolved: from packing more transistors onto a single chip to connecting thousands—or even hundreds of thousands—of chips into a unified fabric across an AI data center. Michael has been advancing the compute frontier for more than four decades, and we’re honored to have him on today’s show. Full ConversationPat Grady: Okay. We’re here with Michael Kagan, the CTO of Nvidia, currently the world’s most valuable company. Michael, thank you for joining us. Michael Kagan: Thank you. My pleasure. Pat Grady: So I thought where we could start—our partner Shaun likes to make the case about every six months that Nvidia would not be Nvidia without Mellanox. Mellanox was a company that you co-founded some 25 years ago, and have been a part of through this day. So can you kind of paint that picture for us? Why is it that the Mellanox acquisition was so critical to Nvidia? Michael Kagan: You know, there was a huge transition in the world in terms of computing and the need for computing. And it grows, grows exponentially. And one of the things that we usually estimate linearly, but the world was exponential. And exponential growth now is actually accelerated. It used to be like Moore’s Law, which is basic silicon, and it was twice every other year. And regardless, the discussion that Moore’s Law in terms of physics is not quite running anymore. Once the AI kicked in, which was in 2010, 2011—kicked in when GPU from graphic processing unit became general processing unit, actually, that’s running workloads where for the first time the AI workload was run on the GPU, taking advantage of the programmability and parallel nature of this machine. The requirements for performance started to grow at a much higher coefficient, so the models started to go up in terms of size and capacity 2X every three months, which requires now 10X or 16X a year performance growth, versus old school of twice every other year. And in order to grow this scale, you need to innovate, and you need to develop solutions at a much higher scale than just basic components. And that’s where the network kicks in, that’s where the network is. And there’s multiple layers of scaling performance that requires high speed networks and high performance networks. The one is what we call scale up. Basically if you’re going back to the CPU days, scaling up was more [inaudible], more transistors, and also some advances in the microarchitecture like out-of-order execution and at some point multicore and so on and so forth. But so this is the basic building block of computing. In the GPU world, the basic building block is the GPU. And in order to scale it up more than you can do on a single piece of silicon with a lot of advances that we are doing with the microarchitecture and advanced technologies, we actually need to do something on the scale of—on the sort of multicore CPU, but a much larger scale. And that’s what we are doing with NVLink. This is a scale-up solution. So our GPU, what we call GPU today, is a rock-sized machine. You need a forklift to lift it. So, you know, if you order just GPU on Amazon, just don’t wonder that you’ll show up this huge rack of … Pat Grady: Yeah, people think chip, but it’s really a system. Michael Kagan: Right. Right. And that’s just one GPU, okay? So basic building block, a very basic computer that application software is running on is this GPU. And it is not just silicon, it’s not just hardware, it’s not just wires, but there is also software layer that exposes CUDA as the API. And that’s what actually enables it to pretty much seamlessly scale. I’m simplifying a little bit the story, but seamlessly scale from one component that used to be a single GPU all the way up to 72, maintaining the same software interface. And once you get this building block as big as it conceivably can be built in terms of power, cost, efficiency, then you start scaling out. And to scale out, it means you take many of these building blocks, connect them together, and now on the algorithm level, on the application level, you actually split your application to multiple pieces running in parallel on these big machines. Pat Grady: Mm-hmm. Michael Kagan: And that’s again where the network comes in. And so if you talk about scale up, we basically made memory like domain to go beyond single compute node and a single GPU. And that’s actually the first thing where Mellanox technology comes in, because before the Mellanox acquisition, the scaling up of Nvidia with the NVLink was limited to a single node machine. Going outside of single compute node, if the 72 GPUs are—it’s actually 36 computers, each one has two GPUs and they’re wired together, so present all this as a single GPU—getting connectivity outside of the signal node, it’s not just plugging in the wire to the connector. It’s a lot of software, it’s a lot of technology within the network, how to make multiple nodes to work as the single machine. And that’s where Mellanox first just immediate in terms of the way we go upstream. That’s the first one. The second one is how do you split the operation across multiple machines? And the way to do it, if I have a task that it takes one GPU to do one second, if I want to accelerate it, I split it to 10, to, you know, a thousand pieces, and send each piece to a different GPU. And now in one millisecond, I get done whatever I was doing in the second. But, you know, you need to communicate this partial job split, split the task, then you need to consolidate the results. And every time you are—and you run this, you know, multiple times, you have multiple iterations or multiple applications running, so that there is a part of it doing communication and part of it doing computation. Now the thing is that you want to split it into as many pieces as you possibly can, because that’s your speed-up factor. But then if your communication is actually blocking you, you waste time, you waste energy, you waste everything. So what you need to do is you need to has a very fast communication. So you split it into many, many pieces, and so each piece takes very little time. But then there is another piece that is communicated, and you need to fit it at this time. So that’s just pure bandwidth. And another thing is that when you tune your application, you tune your application so that communication can be hidden behind computation. And it means that if communication for some reason gets longer, then everybody waits. So it means that what you need to do in the network, you need to have not only just raw performance, like what’s called hero numbers, you know, I can get to that many gigabits per second. I also need to make sure that no matter who communicates to whom, the latency, the time it takes, the distribution is very narrow. So if you look at other network technologies or other network products, you know, you go to the HERO numbers, you know, sending beat from one place to another, it’s basically physics. Pat Grady: Yeah. Michael Kagan: It’s pretty much close to everyone. You know, we are a little bit better, but that’s not the big advantage. But when you do it thousands of times and it takes the same time to do it, versus a very wide distribution of other technologies, then the machine becomes less efficient. So instead of being able to split your job to a thousand GPUs, you can split it only to ten GPUs, because you need to accommodate for the jitter on the network within the computation phase. So inherently, network determines the performance of this cluster. And we look at this data center as basically a single unit of computing. Pat Grady: Yeah. Michael Kagan: Okay? Single unit computing means that you look at this, you start architecting your components, your software and your hardware at the point where this is the data center, this is 100,000 GPUs that we want to make them work together. We need to make multiple chips, compute chips, two, network chips, five. Okay, so this is the scale just in terms of what’s the impact and what’s the investment you need to make to create this single unit of computing. So that’s where Mellanox technology came in. And another aspect of this is we talked about a network that connects the GPUs to run the task. But there is another side of this machine which is customer facing. So this machine needs to serve multiple tenants, and this machine needs to run an operating system. Every computer runs an operating system. Another part of the Mellanox technologies is what we call BlueField DPU, a data processing unit which is actually the computing platform to run the operating system of the data center. In a conventional computer you have a CPU that runs an operating system and runs application software. And there are many things we can talk about, you know, the advantage versus disadvantage. But there are two key things: one is how much time do you spend on your general purpose computing to run the application? You want to maximize it. And another thing is how do you isolate your infrastructure computing from the application computing? Because, you know, viruses and the cyber attacks and so on and so forth. And being able to run infrastructure computing on a different computing platform actually reduces significantly the attack front especially in the side channel attacks, versus what happens if you run it on the same computer. If you remember there was a five or six—well actually, more than almost 10 years ago there was this meltdown and all these cyber attacks of the side channel on CPUs, and this cannot happen, or the attack surface is reduced significantly when you run the different—so on the other side of the network we have also technology. So that’s what makes the data center to be more efficient. And I—well, I may be not objective, but I do agree that this merger of Mellanox and Nvidia, it actually goes both ways. I don’t think that the networking business of, now it’s Nvidia, previously Mellanox, could have been growing that significantly as it grew. Now I think we are the fastest growing ethernet business, you know, let alone NVLink and InfiniBand, but just ethernet business is the fastest-growing business ever. Sonya Huang: What are the things that break as you get to 100,000, maybe eventually a million GPU clusters? And how do you use software to help design around that? Michael Kagan: It’s a multi-stage challenge, okay? One of the things that you need to keep in mind, and it’s not very obvious for all the engineers, that when you design the machine or think how to operate it, well, you know, you have these components and they are working and now just let’s figure out. Okay, so the thing is that the hardware component works at 99.999-whatever percent of the time, and it’s usually okay if you are dealing with a single box with a couple of them. But if you are building a 100,000 component machine or a 100 GPUs machine, which means in terms of components, there is millions of them, the chance that everything works is zero. So something is definitely broken, and you need to design it both from hardware and from software perspective to keep going, to keep going as efficiently as you can, to keep, you know, your performance, you keep your power efficiency and of course keep the service running. So this is challenge number one even before you go to millions. This challenge actually starts at, you know, a few tens of thousands. And that’s number one. Number two is when you are running these workloads, it is really important to—sometimes you run a single job on the entire data center, and then you need to write the software and you need to provide all the interfaces to the software to place the different parts of the jobs more efficiently. Building networks at this scale is a very different story than building—compute network on this scale is a very different story than building just a general purpose data center network. A general purpose data center network is ethernet. It’s not a big deal—well, it is a big deal, but it is a different deal. You are serving, you know, loosely coupled collaborative microservices that create the service that you see as a customer from outside. Here you are running one single application on 100,000 machines, and they need to … Pat Grady: Is that specific to training workloads, or is that also true with inference workloads? Michael Kagan: It’s true for everything. It depends to what scale. And the inference is yet another topic that we [inaudible]. Until recently, training was the key thing, you know, a lot of GPUs. And there was a very specific way of training that was being done. You basically copy this with another model on multiple machines or multiple sets of machines and run them, then consolidate the results and so on and so forth. On the inference, the story is a little bit different, but the thing is that you need to provide the hooks on the hardware and on your low level system software for application and for scheduler to place the job and place the different parts of the job in the most efficient way. And as long as your machine fits in a building, which is about 100,000 GPUs, now we’re talking about a gigawatt, it’s all power driven, then you are here. But the problem is—the challenge is that for many reasons you want to split your workloads across multiple data centers. And sometimes data centers are at a distance of many kilometers, many miles. It may be across the continent. And this comes with yet another challenge, which is the speed of light. Pat Grady: Yeah. Michael Kagan: Okay, now the latency variance between different parts of your machine is dramatically different. And what is even more challenging is that when you talk about networks, the congestion on the network is one of the key problems that deteriorates network performance. And managing congestion across such a latency difference, it’s not like, you know, in the old telco days you put some box at the edge of your data center with a huge buffer and it’s a shock absorber for congestion. A huge buffer  is not good. You know, bigger is not better. There is a famous statement from a very famous woman. And these buffers are basically, or these devices are basically to isolate the external world from the internals. But when you want to run a single workload across data centers that are distant by kilometers, you need to have every machine on one side to be aware. But whom does it communicate to, whether it’s short communication, long communication, and adjust all the communication patterns accordingly, so you don’t need these big buffers. Because big buffers is a jitter. Pat Grady: Yeah. Michael Kagan: And so we have a technology, we actually developed it recently, a technology, all of our ethernet network is Spectrum X. This is the device that we designed and developed based on the Spectrum switch that we put on the edge of the data center. And it provides all the information and telemetry needed for the endpoints to adjust for the congestion. Sonya Huang: Can we talk a little bit more about training versus inference? Like, how does the shape of workload differ when you’re doing, I guess, back prop is a lot more computationally intensive, forward pass less so. But how does the workload differ? And then are you seeing customer demand start to shift from pre-training towards inference, or do you think it’s still very training heavy right now? Pat Grady: And if I could just ask a quick follow-up question with that. Will people be running inference workloads on the same data centers that they use for training, or will these end up being two separate—because they’re different optimizations, people end up using two different sets of data centers? Michael Kagan: Okay. Yeah, that’s a great question, and let me start with the first one. So training has two phases. One is inference, which is just for the propagation and then back propagation to adjust the weights. And for data parallel training, it’s yet another phase to consolidate the results of the weights update across multiple model copies. So until recently it was the main driver of the compute, because until not very long ago—it’s maybe two years, which is ages in the AI era—the inference or AI was mainly perceptional. So you show the picture, that’s a dog. You show the photo of the person, and here that’s Michael and that’s Sonya. And so that’s a single path and that’s it. Then came generative AI, where actually you get the recursive generation. So when you pause the prompt, then it’s not just one inference, it’s many inferences. Because for every token, when you generate text or generate picture, for every new token, you need to go through the entire machine all over again. So instead of one-shot [inaudible] and then there is more. And then now there is reasoning, which means machine starts, you know, sort of thinking. Okay? If you ask me what time is it now, I can tell you. It’s easy, right? What time is it now? But if you ask me a more complicated question, then I need to think, I probably need to wait or compare multiple solutions or multiple paths, and every such a thing is inference. Pat Grady: Yeah. Michael Kagan: Every such thing is inference. And inference itself has actually two phases. One is much more compute intensive, and the other one is memory intensive. It’s what we call prefill. Because when you do the inference, you have some sort of background, which is prompt, which is some relevant data that you need to process and create the context to generate the answer. And this is very compute intensive, it’s not much memory intensive. And the other part is actually generating the answer, which is the decode part of the inference where you generate token by token, okay? Well, there are some technologies that you can generate more than one token, but it’s still a single path is much less than the final answer. So if you combine all these things together, inference demand for computing is actually not less than training, it’s actually even more. And there are two reasons for this. One is that what I explained, that there’s much more computing than it used to be for the inference. The other thing is you train a model once, but you infer many times. You know, ChatGPT, billions of people—or it’s almost billions of people. Customers, they are pounding them all the time in the same model. They trained it once. Sonya Huang: And now making videos. Now they’re making videos. Michael Kagan: Right. Right. Now they’re making videos and you can generate, and then, you know, everybody is doing the inference. My wife, I think she talks to ChatGPT more than to me these days. Once she discovered this, that’s her best friend. Now to your question about machines. You can infer on the phone, okay? So there is definitely going to be much smaller scale installations for inference. It’s like mobile devices. If you look at the data center scale, at the data center scale and its efficiency of the programming, the programmability is much more viable than optimizations for hardware. And, you know, every hardware instance, it has its own cost and its own drawback. So as long as you don’t identify—and I don’t think besides, you know, this—we actually did—it’s a very similar GPU. It’s the same programming model as a GPU for prefill versus decode. I think—I don’t remember when it happened, but actually we announced that we are building the GPU SKU that is optimized for prefill. So you will have—it can do decode, and decode GPU can do prefill, but you can equip your data center with the SKUs or the prefill with the SKUs that are for decode to optimize for typical use. But if your workload shifts for more decode or for more prefill, you can use either one of them to compensate. And this is the importance of programmability. The same interfaces for GPUs, it’s based on CUDA and up, which is—that’s what made Nvidia. Nvidia before Mellanox. Pat Grady: Yeah. Yeah. Can I ask you a question about data center scaling? So for many decades we had Moore’s Law, and chips got more and more dense and produced better and better performance. And then we ran into the laws of physics, and chips just couldn’t get more dense because their quantum mechanical properties caused them to break down. And so then we had to scale up to the rack level and now we got to scale out to the data center level. Is there some analogous law of data center scaling that says when data centers get too big the communication overhead causes the performance to break down? Or just said differently or maybe said more simply: Is there a natural limit to how big data centers can get? Michael Kagan: I think there is a practical limit of how much energy you can consume within the given size of the data center. Pat Grady: If you were surrounded by nuclear power plants and the energy was available, would the data center itself perform? Michael Kagan: I don’t know. I’m not an expert in the construction. But if you surround, there’s energy coming in, now the heat is going out. So there is a whole—we are now basically moved pretty much entirely to the liquid cooling. And one of the reasons we did it is to enable much denser compute power. We couldn’t build as dense computing as we’re building now with air cooling. Pat Grady: Yeah. Michael Kagan: So there’s a whole bunch of technologies coming to help this more and more denser. Now the last big data center which is like XAI scale is 100 or 150 megawatt. Now we’re talking about gigawatt data centers, people are talking about 10 gigawatt data centers. So, you know, looking forward to building much bigger data centers. Sonya Huang: Are you sending the data centers to outer space? Pat Grady: Pretty cool. Michael Kagan: I think—well, one of the things that determines the speed of data center deployment is you know, how fast concrete gets stable. Pat Grady: [laughs] Sonya Huang: So before starting Mellanox, you were at Intel. Michael Kagan: That’s right. Sonya Huang: Sixteen years? Michael Kagan: Sixteen years. Sonya Huang: Became chief architect. Nvidia and Intel recently announced a partnership. Can you share a little bit about what the vision for that might be? Michael Kagan: You know, the starting point is that computing changed in the last decade, or a little bit more than a decade. Nvidia started as the accelerated computing company. Video games was the first. And then it evolved to AI, which is the new way of data processing. So you cannot just—General von Neumann machine just is not capable of being used as a platform to solve the problem like, you know, programming when a machine is just explaining to somebody what to do. Okay, I can explain many things and I can explain to many people what to do, but I can’t explain how to distinguish between cat and dog, right? So there are new challenges that AI solves, and you need acceleration there. And our partnership with Intel is actually fusing accelerated computing with the general purpose computing. Because general purpose computing is not going away. Everything will be accelerated, but we accelerate the general purpose computing, we accelerate the applications. And x86 is the architecture that is dominant there, and it would serve greatly both companies. That’s actually one of the interesting things about Nvidia is the culture of win-win, okay? We are not after taking a bigger piece of the existing pie. We are after baking a bigger pie for everybody, and the success—our success is our customer’s success. Our success is not the failure of our competition. Our success is success of our customers and success of the ecosystem. And I think fusing together conventional computing, von Neumann machines and accelerated computing that are provided with Nvidia, it’s probably opened yet another dimension that I’m not sure what it is, but it basically gives—you know, on the practical short-term view is it gives Nvidia and Intel channels to the market, or expanding the market and serving the markets that otherwise was more challenging. Pat Grady: You mentioned the culture of Nvidia. So when Mellanox became part of Nvidia in 2019, the market cap of the combined company was about $100 billion—which is no joke. But the market cap today is about $4.5 trillion. And so 45x growth in value in six years is pretty phenomenal. How has that changed the culture of Nvidia? How is Nvidia different today now that it’s one of the most admired companies in the world, if not the most admired, versus six years ago? Michael Kagan: Yeah. About this, you know, when we just joined, Jensen was in Israel, and I presented him, you know, that I believe that one plus one will be ten. And I actually was off by a factor of four. Pat Grady: [laughs] Michael Kagan: But, you know, Mellanox and Nvidia in a sense it’s sort of similar, the culture is very similar to begin with, but there are some—there’s nothing absolutely similar. And I was the only founder that left Mellanox after Eyal resigned a few months after the acquisition. And my main focus in the beginning, you know, were things that you think about in the shower, was how to make sure that this acquisition will succeed. Pat Grady: Yeah. Michael Kagan: You know, Nvidia paid $7 billion for a company that I founded and, you know, with all the mixed feelings that were there. But once it’s done, it’s done. Now I have to make it successful. So eventually it worked. Sonya Huang: [laughs] Michael Kagan: Most of the Israeli employees stayed. I think it’s 85 or 90 percent of the original employees stayed. Actually, Nvidia grew more than 2x in Israel in terms of manpower. Pat Grady: Yeah. Michael Kagan: So we’re growing, and we are announcing that we are actually going to build a campus in Israel, a new campus for Nvidia. And so that’s where I think overall the merger was very successful. I did my best to make sure it succeeds. And besides the technology that I was looking at, this part of which is sort of technology, but it’s technology and theology, and there is many other things to make sure that people are comfortable from being in the center of Mellanox, which is the headquarters on Israel, don’t feel left somewhere in the far away with the—and Jensen basically emphasizes the networking is the critical part of Nvidia’s success. Pat Grady: Yeah. Michael Kagan: And he’s right. So I think it was the—it’s considered to be the most successful measure in the history of the technology. You guys probably track the things better than I am, but overall I think it was a great move. Pat Grady: Yeah. Michael Kagan: Looking backwards. Sonya Huang: What are the science fiction things that you spend your time thinking about? I was just even wondering, like, for example, optical interconnects. Do you think that will exist? Do you think AI will ever be better at physics than us and better at data center design than us? Michael Kagan: Well, what I’m thinking, you know, if you look at science fiction, is how to make history to be experimental science. You can, in physics, try something and then see if it works and then try something else. In history, time goes one direction, but you have a good simulation of the world. [inaudible] And we have an Earth 2 climate simulator. And with this type of technology, we can actually simulate how what we do today will impact the global warming 50 years from now, okay? So experimental science, you know, you try something, you see what happens 50 years later. So that’s the science fiction part. And, you know, the physics? Now we are moving from reasoning and so on and so forth. Now once we get AI models to understand physics, we actually can learn physics. AI can teach us physics because the way we get to the laws of physics that we observe—theoretical physics—you observe some phenomena, and you generalize it and you compose the rule that’s basically the law, the physics law that stays underneath this phenomena. And AI is really great at generalizing and data processing and observing, so AI can help us to get to know some laws of physics that we don’t even imagine now. Sonya Huang: Okay, so Huang’s law was 2x every two years. Huang plus Kagan’s law is, what is the slope and how long do you think you can sustain it? Michael Kagan: Well, the slope is somewhere in the range of 10x or a few orders of magnitude a year. Sonya Huang: Okay. Michael Kagan: And that’s what we are doing by the way now, since about two or three years ago we accelerated our product introduction from every other year to every year. Now we introduce a new wave of products every year, and it’s an order of magnitude higher performance. And it’s not on the cheap level performance, it’s on the machine that you can build with this performance. That’s what we are looking at, it’s a single unit of computing. And how long it will stay, I don’t know. I don’t know. But we’ll do our best to maintain it as long as needed and probably even accelerate. It’s all about exponent. It’s all about exponent. It’s hard to imagine. You know, if you look at this Moulay curves or any role curves, they usually plot it on the logarithmic scale so it looks like linear. But that’s the wrong thing to look at. When I’m showing this [inaudible]. So it’s just like this, you know—boom! And a year later it’s the same—boom! You know, you can’t predict what’s going to happen. Who could predict that when iPhone was first introduced or smartphone was first introduced, you know, it’s 15 years ago? Pat Grady: 2007. Michael Kagan: Yeah, 2007. Oh, 17 years ago. Okay, who could imagine that this smartphone, the least-used function, at least for me, is the phone. Pat Grady: Yeah. Michael Kagan: Unless it’s e-commerce, it’s texting, it’s news, it’s mail, it’s basically running your life from this machine. It’s your authentication, your ID is there. So, you know, now who can imagine what’s going to happen, you know, 10 years from now with all these developments that we are doing today? But we are building the platform for innovation. Pat Grady: What is your commentary on who can imagine—notwithstanding, what is the most optimistic view of our future with AI that you like to think about? Like, what could AI do for the world five, ten, fifteen years from now? Michael Kagan: The thing is that Steve Jobs called the computer to be the bicycle of mind. Pat Grady: Yeah. Michael Kagan: Okay? So AI is—it’s maybe, I don’t know if it’s—it’s probably a spaceship. Pat Grady: [laughs] Michael Kagan: Because there’s a lot of things that I would like to do, but I just don’t have enough time, don’t have enough resources to do it. With AI, I will have it. And it doesn’t mean that, you know, I will do twice as much. Maybe I will do 10 times as much. But the thing is that I will want to do a hundred times as much as I want to do today. And, you know, you go to any project leader and nobody says, you know, “I have enough. I have enough manpower, I have enough resources. I don’t need any more.” Okay? If you give him resources which are twice as efficient, he will do four times more. Pat Grady: Yeah. Michael Kagan: And he will want to do 10 times more. So it’s going to—it’s like electricity changes the world, right? Instead of using—you know, in London, you still see these gas lamps and this infrastructure to use the gas as the source of energy. Who could think that, you know, once this electricity was invented, it will change the world that, you know, we can’t live without electricity. The same with AI. Pat Grady: Awesome. Sonya Huang: Beautifully said. Michael Kagan: New world. Sonya Huang: Thank you so much for joining us today. I love this conversation. Michael Kagan: Thank you. Pat Grady: Thank you. Michael Kagan: Thank you for having me. <div class="framer-mcvrsd" id="

Recorded live at Sequoia’s Europe100 event: Michael Kagan, co-founder of Mellanox and CTO of Nvidia, explains how the $7 billion Mellanox acquisition helped transform Nvidia from a chip company into the architect of AI infrastructure. Kagan breaks down the technical challenges of scaling from single GPUs to 100K and eventually million-GPU data centers. He reveals why network performance—not just compute power—determines AI system efficiency. He discusses the shift from training to inference workloads, and his vision for AI as humanity's "spaceship of the mind," and why he thinks AI may help us discover laws of physics we haven’t yet imagined.

Hosted by Sonya Huang and Pat Grady

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