From: peterz@infradead.org
To: Xi Wang <xii@google.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Mel Gorman <mgorman@suse.de>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
suravee.suthikulpanit@amd.com, thomas.lendacky@amd.com
Subject: Re: [PATCH] sched: Make select_idle_sibling search domain configurable
Date: Tue, 28 Jul 2020 12:39:07 +0200 [thread overview]
Message-ID: <20200728103907.GT119549@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200728070131.1629670-1-xii@google.com>
On Tue, Jul 28, 2020 at 12:01:31AM -0700, Xi Wang wrote:
> The scope of select_idle_sibling idle cpu search is LLC. This
> becomes a problem for the AMD CCX architecture, as the sd_llc is only
> 4 cores. On a many core machine, the range of search is too small to
> reach a satisfactory level of statistical multiplexing / efficient
> utilization of short idle time slices.
>
> With this patch idle sibling search is detached from LLC and it
> becomes run time configurable. To reduce search and migration
> overheads, a presearch domain is added. The presearch domain will be
> searched first before the "main search" domain, e.g.:
>
> sysctl_sched_wake_idle_domain == 2 ("MC" domain)
> sysctl_sched_wake_idle_presearch_domain == 1 ("DIE" domain)
>
> Presearch will go through 4 cores of a CCX. If no idle cpu is found
> during presearch, full search will go through the remaining cores of
> a cpu socket.
*groan*, this is horrific :-(
It is also in direct conflict with people wanting to make it smaller.
On top of that, a domain number is a terrible terrible interface. They
aren't even available without SCHED_DEBUG on.
What is the inter-L3 latency? Going by this that had better be awesome.
And if this Infinity Fabric stuff if highly effective in effectively
merging L3s -- analogous to what Intel does with it's cache slices, then
should we not change the AMD topology setup instead of this 'thing'?
Also, this commit:
051f3ca02e46 ("sched/topology: Introduce NUMA identity node sched domain")
seems to suggest L3 is actually bigger. Suravee, can you please comment?
next prev parent reply other threads:[~2020-07-28 10:39 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-28 7:01 [PATCH] sched: Make select_idle_sibling search domain configurable Xi Wang
2020-07-28 10:00 ` kernel test robot
2020-07-28 10:02 ` kernel test robot
2020-07-28 10:39 ` peterz [this message]
2020-07-28 17:54 ` Xi Wang
2020-08-03 22:38 ` Xi Wang
2020-08-04 1:19 ` kernel test robot
2020-08-04 1:19 ` [RFC PATCH] sched: __rebuild_sched_domains() can be static kernel test robot
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=20200728103907.GT119549@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=dietmar.eggemann@arm.com \
--cc=juri.lelli@redhat.com \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mgorman@suse.de \
--cc=mingo@redhat.com \
--cc=rostedt@goodmis.org \
--cc=suravee.suthikulpanit@amd.com \
--cc=thomas.lendacky@amd.com \
--cc=vincent.guittot@linaro.org \
--cc=xii@google.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).