[Beowulf] [EXTERNAL] Re: Deskside clusters

[Jim Cownie]

> Eadline's Law : Cache is only good the second time.

Hmm, that’s why they have all those clever pre-fetchers which try to guess your memory access patterns and predict what's going to be needed next.
(Your choice whether you read “clever” in a cynical voice or not :-))
*IF* that works, then the cache is useful the first time.
If not, then they can mess things up royally by evicting stuff that you did want there.

> On 19 Sep 2021, at 12:02, John Hearns <hearnsj at gmail.com> wrote:
> 
> Eadline's Law : Cache is only good the second time.
> 
> On Fri, 17 Sep 2021, 21:25 Douglas Eadline, <deadline at eadline.org <mailto:deadline at eadline.org>> wrote:
> --snip--
> >
> > Where I disagree with you is (3). Whether or not cache size is important
> > depends on the size of the job. If your iterating through data-parallel
> > loops over a large dataset that exceeds cache size, the opportunity to
> > reread cached data is probably limited or nonexistent. As we often say
> > here, "it depends". I'm sore someone with better low-level hardware
> > knowledge will pipe in and tell me why I'm wrong (Cunningham's Law).
> >
> 
> Of course it all depends. However, as core counts go up, a
> fixed amount of cache must get shared. Since the high core counts
> are putting pressure on main memory BW, cache gets more
> important. This is why AMD is doing V-cache for new processors.
> Core counts have outstripped memory BW, their solution
> seems to be big caches. And, cache is only good the second time :-)
> 
> 
> -- big snip--
> 
> -- 
> Doug
> 
> _______________________________________________
> Beowulf mailing list, Beowulf at beowulf.org <mailto:Beowulf at beowulf.org> sponsored by Penguin Computing
> To change your subscription (digest mode or unsubscribe) visit https://beowulf.org/cgi-bin/mailman/listinfo/beowulf <https://beowulf.org/cgi-bin/mailman/listinfo/beowulf>
> _______________________________________________
> Beowulf mailing list, Beowulf at beowulf.org sponsored by Penguin Computing
> To change your subscription (digest mode or unsubscribe) visit https://beowulf.org/cgi-bin/mailman/listinfo/beowulf

-- Jim
James Cownie <jcownie at gmail.com>
Mob: +44 780 637 7146




-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://beowulf.org/pipermail/beowulf/attachments/20210920/dd518e5e/attachment.htm>