From: Will Deacon <will.deacon@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
mingo@kernel.org, linux-kernel@vger.kernel.org,
valentin.schneider@arm.com, morten.rasmussen@foss.arm.com,
brendan.jackman@arm.com, dietmar.eggemann@arm.com
Subject: Re: [PATCH v2 1/3] sched: Stop nohz stats when decayed
Date: Thu, 8 Feb 2018 16:03:41 +0000 [thread overview]
Message-ID: <20180208160341.GD17775@arm.com> (raw)
In-Reply-To: <20180208154643.GB25181@hirez.programming.kicks-ass.net>
On Thu, Feb 08, 2018 at 04:46:43PM +0100, Peter Zijlstra wrote:
> On Thu, Feb 08, 2018 at 03:30:31PM +0000, Will Deacon wrote:
> > On Thu, Feb 08, 2018 at 03:00:05PM +0100, Peter Zijlstra wrote:
>
> > > Without this ordering I think it would be possible to loose has_blocked
> > > and not observe the CPU either.
> >
> > I had a quick look at this, and I think you're right. This looks very much
> > like an 'R'-shaped test, which means it's smp_mb() all round otherwise Power
> > will go wrong. That also means the smp_mb__after_atomic() in
> > nohz_balance_enter_idle *cannot* be an smp_wmb(), so you might want a
> > comment stating that explicitly.
>
> Thanks Will. BTW, where does that 'R' shape nomenclature come from?
> This is the first I've heard of it.
I don't know where it originates from, but the imfamous "test6.pdf" has it:
https://www.cl.cam.ac.uk/~pes20/ppc-supplemental/test6.pdf
half way down the first page on the left. It says "needs sync+sync" which
is about as bad as it gets for Power (compare with "2+2w", which gets away
with lwsync+lwsync). See also:
http://materials.dagstuhl.de/files/16/16471/16471.DerekWilliams.Slides.pdf
for a light-hearted, yet technically accurate story about the latter.
Will
next prev parent reply other threads:[~2018-02-08 16:03 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-06 19:23 [PATCH v2 0/3] Update blocked load Vincent Guittot
2018-02-06 19:23 ` [PATCH v2 1/3] sched: Stop nohz stats when decayed Vincent Guittot
2018-02-08 12:46 ` Valentin Schneider
2018-02-08 13:15 ` Peter Zijlstra
2018-02-08 13:36 ` Vincent Guittot
2018-02-08 19:21 ` Valentin Schneider
2018-02-09 11:41 ` Vincent Guittot
2018-02-09 12:16 ` Valentin Schneider
2018-02-08 14:00 ` Peter Zijlstra
2018-02-08 14:04 ` Peter Zijlstra
2018-02-08 15:05 ` Vincent Guittot
2018-02-08 15:44 ` Peter Zijlstra
2018-02-08 16:52 ` Vincent Guittot
2018-02-09 12:00 ` Peter Zijlstra
2018-02-08 15:30 ` Will Deacon
2018-02-08 15:46 ` Peter Zijlstra
2018-02-08 16:03 ` Will Deacon [this message]
2018-02-09 9:51 ` Andrea Parri
2018-02-06 19:23 ` [PATCH v2 2/3] sched: reduce the periodic update duration Vincent Guittot
2018-02-06 19:23 ` [PATCH v2 3/3] sched: update blocked load when newly idle Vincent Guittot
2018-02-06 21:25 ` [PATCH v2 0/3] Update blocked load Peter Zijlstra
2018-02-06 21:46 ` Vincent Guittot
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=20180208160341.GD17775@arm.com \
--to=will.deacon@arm.com \
--cc=brendan.jackman@arm.com \
--cc=dietmar.eggemann@arm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=morten.rasmussen@foss.arm.com \
--cc=peterz@infradead.org \
--cc=valentin.schneider@arm.com \
--cc=vincent.guittot@linaro.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;
as well as URLs for NNTP newsgroup(s).