[Beowulf] AMD and AVX512

Sun Jun 20 17:28:25 UTC 2021

I apologize - I should have written earlier, but I don't always work
with my broken right hand. It seems to me that a reasonable basis for
discussing AMD EPYC performance could be the specified performance
data in the Daresburg University benchmark from M.Guest. Yes, newer
versions of AMD EPYC and Xeon Scalable processors have appeared since
then, and new compiler versions. However, Intel already had AVX-512
support, and AMD - AVX-256.
Of course, peak performanceis is not so important as application
performance. There are applications where performance is not limited
to working with vectors - there AVX-512 may not be needed. And in AI
tasks, working with vectors is actual - and GPUs are often used there.
For AI, the Daresburg benchmark, on the other hand, is less relevant.
And in Zen 4, AMD seemed to be going to support 512 bit vectors. But
performance of linear algebra does not always require work with GPU.
In quantum chemistry, you can get acceleration due to vectors on the
V100, let's say a 2 times - how much more expensive is the GPU?
Of course, support for 512 bit vectors is a plus, but you really need
to look to application performance and cost (including power
consumption). I prefer to see to the A64FX now, although there may
need to be rebuild applications. Servers w/A64FX sold now, but the
price is very important.

In message from John Hearns <hearnsj at gmail.com> (Sun, 20 Jun 2021
06:38:06 +0100):
> Regarding benchmarking real world codes on AMD , every year Martyn 
>Guest
> presents a comprehensive set of benchmark studies to the UK Computing
> Insights Conference.
> I suggest a Sunday afternoon with the beverage of your choice is a 
>good
> time to settle down and take time to read these or watch the 
>presentation.
> 
> 2019
> https://www.scd.stfc.ac.uk/SiteAssets/Pages/CIUK-2019-Presentations/Martyn_Guest.pdf
> 
> 
> 2020 Video session
> https://ukri.zoom.us/rec/share/ajvsxdJ8RM1wzpJtnlcypw4OyrZ9J27nqsfAG7eW49Ehq_Z5igat_7gj21Ge8gWu.78Cd9I1DNIjVViPV?startTime=1607008552000
> 
> Skylake / Cascade Lake / AMD Rome
> 
> The slides for 2020 do exist - as I remember all the slides from all 
>talks
> are grouped together, but I cannot find them.
> Watch the video - it is an excellent presentation.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
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> 
> 
> On Sat, 19 Jun 2021 at 16:49, Gerald Henriksen <ghenriks at gmail.com> 
>wrote:
> 
>> On Wed, 16 Jun 2021 13:15:40 -0400, you wrote:
>>
>> >The answer given, and I'm
>> >not making this up, is that AMD listens to their users and gives the
>> >users what they want, and right now they're not hearing any demand 
>>for
>> >AVX512.
>> >
>> >Personally, I call BS on that one. I can't imagine anyone in the HPC
>> >community saying "we'd like processors that offer only 1/2 the 
>>floating
>> >point performance of Intel processors".
>>
>> I suspect that is marketing speak, which roughly translates to not
>> that no one has asked for it, but rather requests haven't reached a
>> threshold where the requests are viewed as significant enough.
>>
>> > Sure, AMD can offer more cores,
>> >but with only AVX2, you'd need twice as many cores as Intel 
>>processors,
>> >all other things being equal.
>>
>> But of course all other things aren't equal.
>>
>> AVX512 is a mess.
>>
>> Look at the Wikipedia page(*) and note that AVX512 means different
>> things depending on the processor implementing it.
>>
>> So what does the poor software developer target?
>>
>> Or that it can for heat reasons cause CPU frequency reductions,
>> meaning real world performance may not match theoritical - thus 
>>easier
>> to just go with GPU's.
>>
>> The result is that most of the world is quite happily (at least for
>> now) ignoring AVX512 and going with GPU's as necessary - particularly
>> given the convenient libraries that Nvidia offers.
>>
>> > I compared a server with dual AMD EPYC >7H12 processors (128)
>> > quad Intel Xeon 8268 >processors (96 cores).
>>
>> > From what I've heard, the AMD processors run much hotter than the 
>>Intel
>> >processors, too, so I imagine a FLOPS/Watt comparison would be even 
>>less
>> >favorable to AMD.
>>
>> Spec sheets would indicate AMD runs hotter, but then again you
>> benchmarked twice as many Intel processors.
>>
>> So, per spec sheets for you processors above:
>>
>> AMD - 280W - 2 processors means system 560W
>> Intel - 205W - 4 processors means system 820W
>>
>> (and then you also need to factor in purchase price).
>>
>> >An argument can be made that for calculations that lend themselves 
>>to
>> >vectorization should be done on GPUs, instead of the main processors 
>>but
>> >the last time I checked, GPU jobs are still memory is limited, and
>> >moving data in and out of GPU memory can still take time, so I can 
>>see
>> >situations where for large amounts of data using CPUs would be 
>>preferred
>> >over GPUs.
>>
>> AMD's latest chips support PCI 4 while Intel is still stuck on PCI 3,
>> which may or may not mean a difference.
>>
>> But what despite all of the above and the other replies, it is AMD 
>>who
>> has been winning the HPC contracts of late, not Intel.
>>
>> * - https://en.wikipedia.org/wiki/Advanced_Vector_Extensions
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> 
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