SXM (socket)

This article is about the socket type. For other uses, see SXM.

Computing node of TSUBAME 3.0 supercomputer showing four NVIDIA Tesla P100 SXM modules

Bare SXM sockets next to sockets with GPUs installed

SXM (Server PCI Express Module) ^[1] is a high bandwidth socket solution for connecting Nvidia Compute Accelerators to a system. Each generation of Nvidia Tesla since P100 models, the DGX computer series and the HGX boards come with an SXM socket type that realizes high bandwidth, power delivery and more for the matching GPU daughter cards. ^[2] Nvidia offers these combinations as an end-user product e.g. in their models of the DGX system series. Current socket generations are SXM for Pascal based GPUs, SXM2 and SXM3 for Volta based GPUs, SXM4 for Ampere based GPUs, and SXM5 for Hopper based GPUs. These sockets are used for specific models of these accelerators, and offer higher performance per card than PCIe equivalents. ^[2] The DGX-1 system was the first to be equipped with SXM-2 sockets and thus was the first to carry the form factor compatible SXM modules with P100 GPUs and later was unveiled to be capable of allowing upgrading to (or being pre-equipped with) SXM2 modules with V100 GPUs. ^{[3] [4]}

SXM boards are typically built with four or eight GPU slots, although some solutions such as the Nvidia DGX-2 connect multiple boards to deliver high performance. While third party solutions for SXM boards exist, most System Integrators such as Supermicro use prebuilt Nvidia HGX boards, which come in four or eight socket configurations. ^[5] This solution greatly lowers the cost and difficulty of SXM based GPU servers, and enables compatibility and reliability across all boards of the same generation.

SXM modules on e.g. HGX boards, particularly recent generations, may have NVLink switches to allow faster GPU-to-GPU communication. This as well reduces bottlenecks which would normally be located within CPU and PCIe. ^{[2] [6]} The GPUs on the daughter cards are just using NVLink as their main communication protocol. For example a Hopper-based H100 SXM5 based GPU can use up to 900GB/s of bandwidth across 18 NVLink 4 channels, with each contributing a 50GB/s of bandwidth; ^[7] This compared to PCIe 5.0, which can handle up to 64GB/s of bandwidth within a x16 slot. ^[8] This high bandwidth also means that GPUs can share memory over the NVLink bus, allowing an entire HGX board to present to the host system as a single, massive GPU. ^[9]

Power delivery is also handled by the SXM socket, negating the need for external power cables such as those needed in PCIe equivalent cards. This, combined with the horizontal mounting allows cooling options of higher efficiency which in turn allows the SXM based GPUs to operate at a much higher TDP. The Hopper-based H100, for example, can draw up to 700W solely from the SXM socket. ^[10] The lack of cabling also makes assembling and repairing of large systems much easier, and also reduces the possible points of failure. ^[2]

The early Nvidia Tegra automotive targeted evaluation board, 'Drive PX2', had two MXM (Mobile PCI Express Module) sockets on both sides of the card, this dual MXM design can be considered a predecessor to the Nvidia Tesla implementation of the SXM socket.

Comparison of accelerators used in DGX: ^{[11] [12] [13]}

Accelerator
H100​
A100 80GB​
A100 40GB​
V100 32GB​
V100 16GB​
P100

Architecture	Socket	FP32 CUDA Cores	FP64 Cores (excl. Tensor)	Mixed INT32/FP32 Cores	INT32 Cores	Boost Clock	Memory Clock	Memory Bus Width	Memory Bandwidth	VRAM	Single Precision (FP32)	Double Precision (FP64)	INT8 (non-Tensor)	INT8 Dense Tensor	INT32	FP16	FP16 Dense Tensor	bfloat16 Dense Tensor	TensorFloat-32 (TF32) Dense Tensor	FP64 Dense Tensor	Interconnect (NVLink)	GPU	L1 Cache Size	L2 Cache Size	TDP	GPU Die Size	Transistor Count	Manufacturing Process
Hopper	SXM5	16896	4608	16896	N/A	1780 MHz	4.8Gbit/s HBM3	5120-bit	3072GB/sec	80GB	60 TFLOPs	30 TFLOPs	N/A	4000 TOPs	N/A	N/A	2000 TFLOPs	2000 TFLOPs	1000 TFLOPs	60 TFLOPs	900GB/sec	GH100	25344KB(192KBx132)	51200 KB	700W	814 mm2	80B	TSMC 4 nm N4
Ampere	SXM4	6912	3456	6912	N/A	1410 MHz	3.2Gbit/s HBM2	5120-bit	2039GB/sec	80GB	19.5 TFLOPs	9.7 TFLOPs	N/A	624 TOPs	19.5 TOPs	78 TFLOPs	312 TFLOPs	312 TFLOPs	156 TFLOPs	19.5 TFLOPs	600GB/sec	GA100	20736KB(192KBx108)	40960 KB	400W	826 mm2	54.2B	TSMC 7 nm N7
Ampere	SXM4	6912	3456	6912	N/A	1410 MHz	2.4Gbit/s HBM2	5120-bit	1555GB/sec	40GB	19.5 TFLOPs	9.7 TFLOPs	N/A	624 TOPs	19.5 TOPs	78 TFLOPs	312 TFLOPs	312 TFLOPs	156 TFLOPs	19.5 TFLOPs	600GB/sec	GA100	20736KB(192KBx108)	40960 KB	400W	826 mm2	54.2B	TSMC 7 nm N7
Volta	SXM3	5120	2560	N/A	5120	1530 MHz	1.75Gbit/s HBM2	4096-bit	900GB/sec	32GB	15.7 TFLOPs	7.8 TFLOPs	62 TOPs	N/A	15.7 TOPs	31.4 TFLOPs	125 TFLOPs	N/A	N/A	N/A	300GB/sec	GV100	10240KB(128KBx80)	6144 KB	350W	815 mm2	21.1B	TSMC 12 nm FFN
Volta	SXM2	5120	2560	N/A	5120	1530 MHz	1.75Gbit/s HBM2	4096-bit	900GB/sec	16GB	15.7 TFLOPs	7.8 TFLOPs	62 TOPs	N/A	15.7 TOPs	31.4 TFLOPs	125 TFLOPs	N/A	N/A	N/A	300GB/sec	GV100	10240KB(128KBx80)	6144 KB	300W	815 mm2	21.1B	TSMC 12 nm FFN
Pascal	SXM/SXM2	N/A	1792	3584	N/A	1480 MHz	1.4Gbit/s HBM2	4096-bit	720GB/sec	16GB	10.6 TFLOPs	5.3 TFLOPs	N/A	N/A	N/A	21.2 TFLOPs	N/A	N/A	N/A	N/A	160GB/sec	GP100	1344KB(24KBx56)	4096 KB	300W	610 mm2	15.3B	TSMC 16 nm FinFET+

References

1. Michael Brown, W.; et al. (2012). "An Evaluation of Molecular Dynamics Performance on the Hybrid Cray XK6 Supercomputer". Procedia Computer Science. 9: 186–195. doi:10.1016/j.procs.2012.04.020.
2. Proud, Matt. "Achieving Maximum Compute Throughput: PCIe vs. SXM2". The Next Platform. Retrieved 2022-03-31.
3. Volta architecture whitepaper nvidia.com
4. DGX 1 User Guide nvidia.com
5. servethehome (2020-05-14). "NVIDIA A100 4x GPU HGX Redstone Platform". ServeTheHome. Retrieved 2022-03-31.
6. "NVLink & NVSwitch for Advanced Multi-GPU Communication". NVIDIA.
7. "Nvidia's H100 – What It Is, What It Does, and Why It Matters". Data Center Knowledge | News and analysis for the data center industry. 2022-03-23. Retrieved 2022-03-31.
8. "Is PCIe 5.0 Worth It? The Benefits of PCIe 5.0 (2022)". www.techreviewer.com. Retrieved 2022-03-31.
9. "NVIDIA HGX A100: Powered by A100 GPUs and NVSwitch". NVIDIA. Retrieved 2022-03-31.
10. "NVIDIA H100 GPU full details: TSMC N4, HBM3, PCIe 5.0, 700W TDP, more". TweakTown. 2022-03-23. Retrieved 2022-03-31.
11. Smith, Ryan (March 22, 2022). "NVIDIA Hopper GPU Architecture and H100 Accelerator Announced: Working Smarter and Harder". AnandTech.
12. Smith, Ryan (May 14, 2020). "NVIDIA Ampere Unleashed: NVIDIA Announces New GPU Architecture, A100 GPU, and Accelerator". AnandTech.
13. "NVIDIA Tesla V100 tested: near unbelievable GPU power". TweakTown. September 17, 2017.

External links

• Erlangen National High Performance Computing Center page on high performance computing with 4x and 8x A100 per computer node, also showing switch topology dumps.