From: Valentin Schneider <firstname.lastname@example.org>
To: Mel Gorman <email@example.com>,
Srikar Dronamraju <firstname.lastname@example.org>
Cc: "Gautham R. Shenoy" <email@example.com>,
Michael Ellerman <firstname.lastname@example.org>,
Michael Neuling <email@example.com>,
Rik van Riel <firstname.lastname@example.org>,
Vincent Guittot <email@example.com>,
Dietmar Eggemann <firstname.lastname@example.org>,
Nicholas Piggin <email@example.com>,
Anton Blanchard <firstname.lastname@example.org>,
Parth Shah <email@example.com>,
Vaidyanathan Srinivasan <firstname.lastname@example.org>,
Subject: Re: [RFC/PATCH] powerpc/smp: Add SD_SHARE_PKG_RESOURCES flag to MC sched-domain
Date: Mon, 12 Apr 2021 11:06:19 +0100 [thread overview]
Message-ID: <email@example.com> (raw)
On 12/04/21 10:37, Mel Gorman wrote:
> On Mon, Apr 12, 2021 at 11:54:36AM +0530, Srikar Dronamraju wrote:
>> * Gautham R. Shenoy <firstname.lastname@example.org> [2021-04-02 11:07:54]:
>> > To remedy this, this patch proposes that the LLC be moved to the MC
>> > level which is a group of cores in one half of the chip.
>> > SMT (SMT4) --> MC (Hemisphere)[LLC] --> DIE
>> I think marking Hemisphere as a LLC in a P10 scenario is a good idea.
>> > While there is no cache being shared at this level, this is still the
>> > level where some amount of cache-snooping takes place and it is
>> > relatively faster to access the data from the caches of the cores
>> > within this domain. With this change, we no longer see regressions on
>> > P10 for applications which require single threaded performance.
>> Peter, Valentin, Vincent, Mel, etal
>> On architectures where we have multiple levels of cache access latencies
>> within a DIE, (For example: one within the current LLC or SMT core and the
>> other at MC or Hemisphere, and finally across hemispheres), do you have any
>> suggestions on how we could handle the same in the core scheduler?
> Minimally I think it would be worth detecting when there are multiple
> LLCs per node and detecting that in generic code as a static branch. In
> select_idle_cpu, consider taking two passes -- first on the LLC domain
> and if no idle CPU is found then taking a second pass if the search depth
> allows within the node with the LLC CPUs masked out.
I think that's actually a decent approach. Tying SD_SHARE_PKG_RESOURCES to
something other than pure cache topology in a generic manner is tough (as
it relies on murky, ill-defined hardware fabric properties).
Last I tried thinking about that, I stopped at having a core-to-core
latency matrix, building domains off of that, and having some knob
specifying the highest distance value below which we'd set
SD_SHARE_PKG_RESOURCES. There's a few things I 'hate' about that; for one
it makes cpus_share_cache() somewhat questionable.
> While there would be
> a latency hit because cache is not shared, it would still be a CPU local
> to memory that is idle. That would potentially be beneficial on Zen*
> as well without having to introduce new domains in the topology hierarchy.
> Mel Gorman
> SUSE Labs
next prev parent reply other threads:[~2021-04-12 10:08 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-02 5:37 [RFC/PATCH] powerpc/smp: Add SD_SHARE_PKG_RESOURCES flag to MC sched-domain Gautham R. Shenoy
2021-04-02 7:36 ` Gautham R Shenoy
2021-04-12 6:24 ` Srikar Dronamraju
2021-04-12 9:37 ` Mel Gorman
2021-04-12 10:06 ` Valentin Schneider [this message]
2021-04-12 10:48 ` Mel Gorman
2021-04-19 6:14 ` Gautham R Shenoy
2021-04-12 12:21 ` Vincent Guittot
2021-04-12 15:24 ` Mel Gorman
2021-04-12 16:33 ` Michal Suchánek
2021-04-14 7:02 ` Gautham R Shenoy
2021-04-13 7:10 ` Vincent Guittot
2021-04-14 7:00 ` Gautham R Shenoy
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).