From: Mike Galbraith <umgwanakikbuti@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Steinar H. Gunderson" <sgunderson@bigfoot.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: bisected: futex regression >= 3.14 - was - Slowdown due to threads bouncing between HT cores
Date: Wed, 08 Oct 2014 19:59:44 +0200 [thread overview]
Message-ID: <1412791184.5173.11.camel@marge.simpson.net> (raw)
In-Reply-To: <CA+55aFyuH07zzD6dD4k0pdyvJ7fUhFdFrmPYJi9W=FtHihgndA@mail.gmail.com>
On Wed, 2014-10-08 at 13:04 -0400, Linus Torvalds wrote:
> On Wed, Oct 8, 2014 at 11:37 AM, Mike Galbraith
> <umgwanakikbuti@gmail.com> wrote:
> >
> > 11d4616bd07f38d496bd489ed8fad1dc4d928823 is the first bad commit
> > commit 11d4616bd07f38d496bd489ed8fad1dc4d928823
> > Author: Linus Torvalds <torvalds@linux-foundation.org>
> > Date: Thu Mar 20 22:11:17 2014 -0700
> >
> > futex: revert back to the explicit waiter counting code
>
> While that revert might make things a tiny bit slower (I hated doing
> it, but the clever approach sadly didn't work on powerpc and depended
> on x86 locking semantics), I seriously doubt it's really relevant.
> It's more likely that the *real* problem itself is very
> timing-dependent, and the subtle synchronization changes here then
> expose it or hide it, rather than really fixing anything.
>
> So like Thomas, I would suspect a race condition in the futex use, and
> then the exact futex implementation details are just exposing it
> incidentally.
Whew, good, futex.c is hard. Heads up chess guys <punt>.
-Mike
next prev parent reply other threads:[~2014-10-08 17:59 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-03 19:44 Steinar H. Gunderson
2014-10-03 21:11 ` Marc Burkhardt
2014-10-03 21:14 ` Steinar H. Gunderson
2014-10-04 9:22 ` Marc Burkhardt
2014-10-04 13:41 ` Andi Kleen
2014-10-04 14:12 ` Steinar H. Gunderson
2014-10-04 14:50 ` Chuck Ebbert
2014-10-05 11:19 ` Steinar H. Gunderson
2014-10-08 15:37 ` bisected: futex regression >= 3.14 - was - " Mike Galbraith
2014-10-08 16:14 ` Thomas Gleixner
2014-10-08 16:45 ` Steinar H. Gunderson
2014-10-08 17:52 ` Mike Galbraith
2014-10-08 16:23 ` Steinar H. Gunderson
2014-10-08 17:04 ` Linus Torvalds
2014-10-08 17:05 ` Steinar H. Gunderson
2014-10-08 17:59 ` Mike Galbraith [this message]
2014-10-24 15:25 ` Thomas Gleixner
2014-10-24 16:38 ` Mike Galbraith
2014-10-26 10:39 ` Steinar H. Gunderson
2014-10-26 13:16 ` Mike Galbraith
2014-10-26 13:58 ` Mike Galbraith
2014-10-26 14:11 ` Steinar H. Gunderson
2014-10-26 14:41 ` Mike Galbraith
2014-10-27 10:05 ` Mike Galbraith
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=1412791184.5173.11.camel@marge.simpson.net \
--to=umgwanakikbuti@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=peterz@infradead.org \
--cc=sgunderson@bigfoot.com \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.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
Powered by JetHome