From: Mel Gorman <mgorman@techsingularity.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>,
Davidlohr Bueso <dave@stgolabs.net>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: Loadavg accounting error on arm64
Date: Mon, 16 Nov 2020 17:24:44 +0000 [thread overview]
Message-ID: <20201116172444.GV3371@techsingularity.net> (raw)
In-Reply-To: <20201116164928.GF3121392@hirez.programming.kicks-ass.net>
On Mon, Nov 16, 2020 at 05:49:28PM +0100, Peter Zijlstra wrote:
> > So while we might be able to avoid a smp_rmb() before the read of
> > sched_contributes_to_load and rely on p->on_cpu ordering there,
> > we may still need a smp_wmb() after nr_interruptible() increments
> > instead of waiting until the smp_store_release() is hit while a task
> > is scheduling. That would be a real memory barrier on arm64 and a plain
> > compiler barrier on x86-64.
>
Wish I read this before sending the changelog
> I'm mighty confused by your words here; and the patch below. What actual
> scenario are you worried about?
>
The wrong one apparently. Even if the IRQ is released, the IPI would
deliver to the CPU that should observe the correct value or take the
other path when smp_cond_load_acquire(&p->on_cpu, !VAL) waits for the
schedule to finish so I'm now both confused and wondering why smp_wmb
made a difference at all.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2020-11-16 17:25 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-16 9:10 Loadavg accounting error on arm64 Mel Gorman
2020-11-16 11:49 ` Mel Gorman
2020-11-16 12:00 ` Mel Gorman
2020-11-16 12:53 ` Peter Zijlstra
2020-11-16 12:58 ` Peter Zijlstra
2020-11-16 15:29 ` Mel Gorman
2020-11-16 16:42 ` Mel Gorman
2020-11-16 16:49 ` Peter Zijlstra
2020-11-16 17:24 ` Mel Gorman [this message]
2020-11-16 17:41 ` Will Deacon
2020-11-16 12:46 ` Peter Zijlstra
2020-11-16 12:58 ` Mel Gorman
2020-11-16 13:11 ` Will Deacon
2020-11-16 13:37 ` Mel Gorman
2020-11-16 14:20 ` Peter Zijlstra
2020-11-16 15:52 ` Mel Gorman
2020-11-16 16:54 ` Peter Zijlstra
2020-11-16 17:16 ` Mel Gorman
2020-11-16 19:31 ` Mel Gorman
2020-11-17 8:30 ` [PATCH] sched: Fix data-race in wakeup Peter Zijlstra
2020-11-17 9:15 ` Will Deacon
2020-11-17 9:29 ` Peter Zijlstra
2020-11-17 9:46 ` Peter Zijlstra
2020-11-17 10:36 ` Will Deacon
2020-11-17 12:52 ` Valentin Schneider
2020-11-17 15:37 ` Valentin Schneider
2020-11-17 16:13 ` Peter Zijlstra
2020-11-17 19:32 ` Valentin Schneider
2020-11-18 8:05 ` Peter Zijlstra
2020-11-18 9:51 ` Valentin Schneider
2020-11-18 13:33 ` Marco Elver
2020-11-17 9:38 ` [PATCH] sched: Fix rq->nr_iowait ordering Peter Zijlstra
2020-11-17 11:43 ` Mel Gorman
2020-11-19 9:55 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2020-11-17 12:40 ` [PATCH] sched: Fix data-race in wakeup Mel Gorman
2020-11-19 9:55 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
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=20201116172444.GV3371@techsingularity.net \
--to=mgorman@techsingularity.net \
--cc=dave@stgolabs.net \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=peterz@infradead.org \
--cc=will@kernel.org \
/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