[Beowulf] Memory latency (was woodcrest)
Kozin, I (Igor)
i.kozin at dl.ac.uk
Fri Aug 18 04:07:54 PDT 2006
These are long integers, right? Otherwise the array could almost
fit into 4MB cache of Itanium or Woodcrest.
However even this would not be enough for Power5 which has a massive
36 MB L3 cache. By the way, we have Power5 and PowerPC available if you want.
> I wrote a pthread based latency tester that will access N integers
> randomly per thread. Each member of the array is accessed once.
> All the numbers below are for N=1,000,000 integers. Every integer is
> loaded exactly once, randomly.
> The first number is the latency per thread, so it increases with memory
> contention. The second number is the "effective" ns, where I divide
> the run time of all threads and divide it by the integers retreived.
> It should decrease with increased threads if the machine has the CPU
> and memory system parallelism to avoid contention.
> 1 thread 2 threads 4 threads
> Dual Opteron 275 83.69ns/83.69ns 80ns/52.08ns 85ns/21.72ns
> Quad opteron 846 108.07/108.07ns 115ns/61.39ns 110ns/27.89ns
> Dual Woodcrest-2.66 107.18/107.18ns 108ns/54.03ns 118ns/29.69ns
> Dual core amd64-2.2GHz 89.45/89.45ns 89.45ns/44.72 145ns/52.76ns
> AMD64 3200-2.0GHz 69.74ns/69.74ns 69ns/69.31ns 137ns/69.85ns
> Dual socket nacoma 3.4GHz 130.45/130.45ns 133/66.72ns 230ns/67.72ns
> Dual core p4-3.0 115.45/115.46ns 185ns/101.03ns 283ns/92.67ns
> Dual it2-1.4GHz 200.47/200.47ns 203ns/101.92ns 362ns/101.57ns
> I'm happy to say that Pathscale, Intel, GCC-3, and GCC-4 all share
> mostly identical performance. Although, I had to be very careful with
> pathscale to avoid the benchmark routine from getting optimized away.
> Anyone have a Rev F opteron handy?
>  Where runtime = max(finishtimes)-min(starttimes)
>  Dual socket, dual core = 4 cores
>  Quad socket, single core = 4 cores
>  Single core/single socket = 1 core
>  Dual core/single socket = 2 cores
>  Dual socket, single core = 2 cores.
> Bill Broadley
> Computational Science and Engineering
> UC Davis
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