[Beowulf] [External] Re: AMD and AVX512

Prentice Bisbal pbisbal at pppl.gov
Mon Jun 21 20:56:08 UTC 2021

Thanks for the input. I have looked at that Wikipedia page before, but 
never checked it that closely. I just looked mainly to see what 
processors supported what extensions. After taking a closer look at 
AVX-512, and all the different subdivisions, I see exactly what you're 
saying. It's a mess! Compare that to AVX and AVX2, where it's an 
all-or-nothing thing. Makes a lot more sense.


On 6/19/21 11:49 AM, Gerald Henriksen 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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