[Beowulf] AMD and AVX512

[Stu Midgley]

we should be upto about EV12 by now...

On Sun, Jun 20, 2021 at 1:38 PM John Hearns <hearnsj at gmail.com> wrote:

> 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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-- 
Dr Stuart Midgley
sdm900 at gmail.com
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