[Beowulf] [EXTERNAL] Re: Deskside clusters

[John Hearns]

Over on the Julia discussion list there are often topics on performance or
varying performance - these often turn out to be due to the BLAS libraries
in use, and how they are being used.
I believe that there is a project for pureJulia BLAS.

On Mon, 20 Sept 2021 at 18:41, Lux, Jim (US 7140) via Beowulf <
beowulf at beowulf.org> wrote:

>
>
>
>
> *From: *Beowulf <beowulf-bounces at beowulf.org> on behalf of Lawrence
> Stewart <stewart at serissa.com>
> *Date: *Monday, September 20, 2021 at 9:17 AM
> *To: *Jim Cownie <jcownie at gmail.com>
> *Cc: *Lawrence Stewart <stewart at serissa.com>, Douglas Eadline <
> deadline at eadline.org>, "beowulf at beowulf.org" <beowulf at beowulf.org>
> *Subject: *Re: [Beowulf] [EXTERNAL] Re: Deskside clusters
>
>
>
> Well said.  Expanding on this, caches work because of both temporal
> locality and
>
> spatial locality.  Spatial locality is addressed by having cache lines be
> substantially
>
> larger than a byte or word.  These days, 64 bytes is pretty common.  Some
> prefetch schemes,
>
> like the L1D version that fetches the VA ^ 64 clearly affect spatial
> locality.  Streaming
>
> prefetch has an expanded notion of “spatial” I suppose!
>
>
>
> What puzzles me is why compilers seem not to have evolved much notion of
> cache management. It
>
> seems like something a smart compiler could do.  Instead, it is left to
> Prof. Goto and the folks
>
> at ATLAS and BLIS to figure out how to rewrite algorithms for efficient
> cache behavior. To my
>
> limited knowledge, compilers don’t make much use of PREFETCH or any
> non-temporal loads and stores
>
> either. It seems to me that once the programmer helps with RESTRICT and so
> forth, then compilers could perfectly well dynamically move parts of arrays
> around to maximize cache use.
>
>
>
> -L
>
>
>
> I suspect that there’s enough variability among cache implementation and
> the wide variety of algorithms that might use it that writing a
> smart-enough compiler is “hard” and “expensive”.
>
>
>
> Leaving it to the library authors is probably the best “bang for the
> buck”.
>
>
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