Cloudflare Cloudflare Outlines Gen X servers - AMD EPYC 7642 based

eva2000 · Feb 24, 2020

Cloudflare blog has outlined their new Gen X servers powered by AMD EPYC 7642 zen2 Rome based cpus which have 48 physical cpu cores + 48 virtual cpu cores to total 96 cpu threads Cloudflare’s Gen X: Servers for an Accelerated Future

CPU efficiency is very important to our server design. Since we have a compute-heavy workload, our servers are typically limited by the CPU before other components. Cloudflare’s software stack scales quite well with additional cores. So, we care more about core-count and power-efficiency than dimensions such as clock speed.

We selected the AMD EPYC 7642 processor in a single-socket configuration for Gen X. This CPU has 48-cores (96 threads), a base clock speed of 2.4 GHz, and an L3 cache of 256 MB. While the rated power (225W) may seem high, it is lower than the combined TDP in our Gen 9 servers and we preferred the performance of this CPU over lower power variants. Despite AMD offering a higher core count option with 64-cores, the performance gains for our software stack and usage weren’t compelling enough.

We have deployed the AMD EPYC 7642 in half a dozen Cloudflare data centers; it is considerably more powerful than a dual-socket pair of high-core count Intel processors (Skylake as well as Cascade Lake) we used in the last generation.

Readers of our blog might remember our excitement around ARM processors. We even ported the entirety of our software stack to run on ARM, just as it does with x86, and have been maintaining that ever since even though it calls for slightly more work for our software engineering teams. We did this leading up to the launch of Qualcomm’s Centriq server CPU, which eventually got shuttered. While none of the off-the-shelf ARM CPUs available this moment are interesting to us, we remain optimistic about high core count offerings launching in 2020 and beyond, and look forward to a day when our servers are a mix of x86 (Intel and AMD) and ARM.

We aim to replace servers when the efficiency gains enabled by new equipment outweigh their cost.

The performance we’ve seen from the AMD EPYC 7642 processor has encouraged us to accelerate replacement of multiple generations of Intel-based servers.
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For memory, we continued to use 256GB of RAM, as in our prior generation, but rated higher at 2933MHz. For storage, we continue to have ~3TB, but moved to 3x1TB form factor using NVME flash (instead of SATA) with increased available IOPS and higher endurance, which enables full disk encryption using LUKS without penalty. For the network card, we continue to use Mellanox 2x25G NIC.
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We moved from our multi-node chassis back to a simple 1U form factor, designed to be lighter and less error prone during operational work at the data center. We also added multiple new ODM partners to diversify how we manufacture our equipment and to take advantage of additional global warehousing.
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with subsequent blog posts to come outlining the performance of their AMD EPYC 7642 Gen X servers

Our Gen X server is intentionally designed with an “empty” PCIe slot for a potential add on card, if it can perform some functions more efficiently than the primary CPU. Would that be a GPU, FPGA, SmartNIC, custom ASIC, TPU or something else? We’re intrigued to explore the possibilities.

In accompanying blog posts over the next few days, our hardware engineers will describe how AMD 7642 performed against the benchmarks we care about. We are thankful for their hard work.
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Phoronix folks also benchmarked AMD EPYC 7642 recently too AMD EPYC 7642 Benchmarks: The Rome 48 Core CPU That Easily Takes On Intel's Xeon Platinum 8280 Review - Phoronix

eva2000 · Feb 26, 2020

New Cloudflare blog post at An EPYC trip to Rome: AMD is Cloudflare's 10th-generation Edge server CPU

More than 1 billion unique IP addresses pass through the Cloudflare Network each day, serving on average 11 million HTTP requests per second and operating within 100ms of 95% of the Internet-connected population globally. Our network spans 200 cities in more than 90 countries, and our engineering teams have built an extremely fast and reliable infrastructure.

We’re extremely proud of our work and are determined to help make the Internet a better and more secure place. Cloudflare engineers who are involved with hardware get down to servers and their components to understand and select the best hardware to maximize the performance of our stack.

Our software stack is compute intensive and is very much CPU bound, driving our engineers to work continuously at optimizing Cloudflare’s performance and reliability at all layers of our stack. With the server, a straightforward solution for increasing computing power is to have more CPU cores. The more cores we can include in a server, the more output we can expect. This is important for us since the diversity of our products and customers has grown over time with increasing demand that requires our servers to do more. To help us drive compute performance, we needed to increase core density and that's what we did. Below is the processor detail for servers we’ve deployed since 2015, including the core counts:

In 2018, we made a big jump in total number of cores per server with Gen 9. Our physical footprint was reduced by 33% compared to Gen 8, giving us increased capacity and computing power per rack. Thermal Design Power (TDP aka typical power usage) are mentioned above to highlight that we've also been more power efficient over time. Power efficiency is important to us: first, because we'd like to be as carbon friendly as we can; and second, so we can better utilize our provisioned power supplied by the data centers. But we know we can do better.

Our main defining metric is Requests per Watt. We can increase our Requests per Second number with more cores, but we have to stay within our power budget envelope. We are constrained by the data centers’ power infrastructure which, along with our selected power distribution units, leads us to power cap for each server rack. Adding servers to a rack obviously adds more power draw increasing power consumption at the rack level. Our Operational Costs significantly increase if we go over a rack’s power cap and have to provision another rack. What we need is more compute power inside the same power envelope which will drive a higher (better) Requests per Watt number – our key metric.

As you might imagine, we look at power consumption carefully in the design stage. From the above you can see that it’s not worth the time for us to deploy more power-hungry CPUs if TDP per Core is higher than our current generation which would hurt our Requests per Watt metric. As we started looking at production ready systems to power our Gen X solution, we took a long look at what is available to us in the market today and we’ve made our decision. We’re moving on from Gen 9's 48-core setup of dual socket Intel® Xeon® Platinum 6162's to a 48-core single socket AMD EPYC™ 7642.
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eva2000 · Feb 27, 2020

3rd Cloudflare blog article Impact of Cache Locality

This time around, we have taken steps to understand our workloads at the hardware level through the use of hardware performance counters and profiling tools. Using these specialized CPU registers and profilers, we collected data on the AMD 2nd Gen EPYC and Intel Skylake-based Xeon processors in a lab environment, then validated our observations in production against other generations of servers from the past.
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We evaluated several Intel Cascade Lake and AMD 2nd Gen EPYC processors, trading off various factors between power and performance; the AMD EPYC 7642 CPU came out on top. The majority of Cascade Lake processors have 1.375 MiB L3 cache per core shared across all cores, a common theme that started with Skylake. On the other hand, the 2nd Gen EPYC processors start at 4 MiB per core. The AMD EPYC 7642 is a unique SKU since it has 256 MiB of L3 cache shared across its 48 cores. Having a cache this large or approximately 5.33 MiB sitting right next to each core means that a program will spend fewer cycles fetching data from RAM with the capability to have more data readily available in the L3 cache.

Traditional cache layout has also changed with the introduction of 2nd Gen EPYC, a byproduct of AMD using a multi-chip module (MCM) design. The 256 MiB L3 cache is formed by 8 individual dies or Core Complex Die (CCD) that is formed by 2 Core Complexes (CCX) with each CCX containing 16 MiB of L3 cache.
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Results
The 1P AMD 2nd Gen EPYC 7642 powered server took the lead and processed 50% more requests per second compared to our Gen 9’s 2P Intel Xeon Platinum 6162 server.

We are running a sustained workload, so we should end up with a sustained operating frequency that is higher than base clock. The AMD EPYC 7642 operating frequency or the number cycles that the processor had at its disposal was approximately 20% greater than the Intel Xeon Platinum 6162, so frequency alone was not enough to explain the 50% gain in requests per second.
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Then they looked at several generations of their servers

We put the 2nd Gen EPYC-based Gen X into production with hopes that the results would mirror closely to what we have previously seen in the lab. We found that the requests per second did not quite align with the results we had hoped, but the AMD EPYC server still outperformed all previous generations including outperforming the Intel Gen 9 server by 36%.
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Sustained operating frequency was nearly identical to what we have seen back in the lab.
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Due to the lower than expected requests per second, we also saw lower instructions retired over time and higher L3 cache miss rate but maintained a lead over Gen 9, with 29% better performance.
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eva2000 · Feb 28, 2020

4th Cloudflare blog post Gen X Performance Tuning

We are using AMD 2nd Gen EPYC 7642 for our tenth generation “Gen X” servers. We found many aspects of this processor compelling such as its increase in performance due to its frequency bump and cache-to-core ratio. We have partnered with AMD to get the best performance out of this processor and today, we are highlighting our tuning efforts that led to an additional 6% performance.
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eva2000 · Feb 29, 2020

Cloudflare blog post #5 Securing Memory at EPYC Scale

At Cloudflare, we encrypt data both in transit (on the network) and at rest (on the disk). Both practices address some of the most common vectors used to exfiltrate information and these measures serve to protect sensitive data from attackers but, what about data currently in use?

Can encryption or any technology eliminate all threats? No, but as Infrastructure Security, it’s our job to consider worst-case scenarios. For example, what if someone were to steal a server from one of our data centers? How can we leverage the most reliable, cutting edge, innovative technology to secure all data on that host if it were in the wrong hands? Would it be protected? And, in particular, what about the server’s RAM?

Data in random access memory (RAM) is usually stored in the clear. This can leave data vulnerable to software or hardware probing by an attacker on the system. Extracting data from memory isn’t an easy task but, with the rise of persistent memory technologies, additional attack vectors are possible:

Dynamic random-access memory (DRAM) interface snooping

Installation of hardware devices that access host memory

Freezing and stealing dual in-line memory module (DIMMs)

Stealing non-volatile dual in-line memory module (NVDIMMs)

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Since we are using AMD for our tenth generation "Gen X servers", we found an interesting security feature within the System on a Chip architecture of the AMD EPYC line. Secure Memory Encryption (SME) is an x86 instruction set extension introduced by AMD and available in the EPYC processor line. SME provides the ability to mark individual pages of memory as encrypted using standard x86 page tables. A page that is marked encrypted will be automatically decrypted when read from DRAM and encrypted when written to DRAM. SME can therefore be used to protect the contents of DRAM from physical attacks on the system.
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eva2000 · Mar 2, 2020

Cloudflare blog post #6 Technical Details of Why Cloudflare Chose AMD EPYC for Gen X Servers which is just a summary of the previous 5 blog posts

In the meantime, we've deployed AMD's EPYC processors as part of Gen X server platform and for the first time are not using any Intel components at all. This week, we announced details of this tenth generation of servers. Below is a recap of why we're excited about the design, specifications, and performance of our newest hardware.
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Compared with our prior server (Gen 9), our Gen X server processes as much as 36% more requests while costing substantially less. Additionally, it enables a ~50% decrease in L3 cache miss rate and up to 50% decrease in NGINX p99 latency, powered by a CPU rated at 25% lower TDP (thermal design power) per core.
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