From: Vincent Guittot <vincent.guittot@linaro.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
"Gautham R. Shenoy" <ego@linux.vnet.ibm.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Michael Neuling <mikey@neuling.org>,
Rik van Riel <riel@surriel.com>,
Valentin Schneider <valentin.schneider@arm.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Nicholas Piggin <npiggin@gmail.com>,
Anton Blanchard <anton@ozlabs.org>,
Parth Shah <parth@linux.ibm.com>,
Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
LKML <linux-kernel@vger.kernel.org>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [RFC/PATCH] powerpc/smp: Add SD_SHARE_PKG_RESOURCES flag to MC sched-domain
Date: Mon, 12 Apr 2021 14:21:47 +0200 [thread overview]
Message-ID: <CAKfTPtDX-p=gWAVgYzLNCNuQ2e=QP2pTeMs=BmNBo31fpGKxrg@mail.gmail.com> (raw)
In-Reply-To: <20210412093722.GS3697@techsingularity.net>
On Mon, 12 Apr 2021 at 11:37, Mel Gorman <mgorman@techsingularity.net> wrote:
>
> On Mon, Apr 12, 2021 at 11:54:36AM +0530, Srikar Dronamraju wrote:
> > * Gautham R. Shenoy <ego@linux.vnet.ibm.com> [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?
I would say that SD_SHARE_PKG_RESOURCES is there for that and doesn't
only rely on cache
> >
>
> 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
We have done a lot of changes to reduce and optimize the fast path and
I don't think re adding another layer in the fast path makes sense as
you will end up unrolling the for_each_domain behind some
static_banches.
SD_SHARE_PKG_RESOURCES should be set to the last level where we can
efficiently move task between CPUs at wakeup
> allows within the node with the LLC CPUs masked out. 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.
What is the current sched_domain topology description for zen ?
>
> --
> Mel Gorman
> SUSE Labs
next prev parent reply other threads:[~2021-04-12 12:22 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
2021-04-12 10:48 ` Mel Gorman
2021-04-19 6:14 ` Gautham R Shenoy
2021-04-12 12:21 ` Vincent Guittot [this message]
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
Reply instructions:
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:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAKfTPtDX-p=gWAVgYzLNCNuQ2e=QP2pTeMs=BmNBo31fpGKxrg@mail.gmail.com' \
--to=vincent.guittot@linaro.org \
--cc=anton@ozlabs.org \
--cc=dietmar.eggemann@arm.com \
--cc=ego@linux.vnet.ibm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mgorman@techsingularity.net \
--cc=mikey@neuling.org \
--cc=mpe@ellerman.id.au \
--cc=npiggin@gmail.com \
--cc=parth@linux.ibm.com \
--cc=riel@surriel.com \
--cc=srikar@linux.vnet.ibm.com \
--cc=svaidy@linux.vnet.ibm.com \
--cc=valentin.schneider@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* 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).