Sandra 2013: Measuring GP Cache and Memory Latencies

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Sandra 2013: Measuring GP Cache and Memory Latencies

Postby Apoptosis » Tue Nov 13, 2012 10:21 am

gp_lat_global.png
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We've launched a new benchmark in Sandra 2013: GP GPU/APU Cache and Memory Latency benchmark.

While it works on the same principle as the System Memory Latency benchmark you know (and love?), as GPUs are different from CPUs - some things are not quite the same.


Here is an article to clarify its operation through concrete examples: the different kinds of GP memory (global, constant, shared, private, texture), how the latency is measured through the different access patterns (full random, in-page random, sequential/linear), how TLB caches affect latencies, etc.


http://www.sisoftware.net/?d=qa&f=gpu_mem_latency


GPUs are somewhat more secretive than CPUs, with the different cache levels and types not always published - even less the latencies of various levels. While nVidia's specific architectures (G80, GT200) have been analysed though micro-benchmarking in CUDA before - here Sandra can benchmark and contrast different architectures of GPUs and APUs from different vendors through OpenCL (and CUDA).

Unlike yourselves we don't have many devices to test - but even the 4 devices tested here (2 GPU, 2 APU from different vendors) show pretty interesting results.

We've used the very results to improve our own benchmarks in Sandra 2013 (GP Cryptography - AES encrypt/decrypt kernels) with significant gains (+25-40%) especially on AMD and Intel. (details in next article ;)

While the optimisation is somewhat simple, it is not that obvious without the latency data: we have worked with both vendors on the previous version and nobody thought of it. So it may be more useful than it first appears.
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