From: Ingo Molnar <mingo@kernel.org>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Mel Gorman <mgorman@techsingularity.net>,
Peter Zijlstra <peterz@infradead.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Chris Mason <clm@fb.com>, Darren Hart <dvhart@linux.intel.com>,
Hugh Dickins <hughd@google.com>,
linux-kernel@vger.kernel.org, Davidlohr Bueso <dbueso@suse.de>,
Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH v5] futex: Remove requirement for lock_page in get_futex_key
Date: Sat, 6 Feb 2016 09:22:14 +0100 [thread overview]
Message-ID: <20160206082214.GA29946@gmail.com> (raw)
In-Reply-To: <20160205180239.GB12375@linux-uzut.site>
* Davidlohr Bueso <dave@stgolabs.net> wrote:
> On Fri, 05 Feb 2016, Ingo Molnar wrote:
>
> >So I too didn't understand that sentence at first, because the capitalization
> >really throws off quick parsing of that comment, as 'MB' ususally denotes
> >megabytes.
>
> Sure, fair enough.
>
> >
> >So please change it to "mb(); (A)" or so - and I think all of these comments
> >should be changed to use a standard API name for the barrier they imply, as the
> >head of futex.c does:
> >
> >* waiters++; (a)
> >* mb(); (A) <-- paired with -.
> >* |
> >* lock(hash_bucket(futex)); |
> >* |
> >* uval = *futex; |
> >* | *futex = newval;
> >* | sys_futex(WAKE, futex);
> >* | futex_wake(futex);
> >* |
> >* `-------> mb(); (B)
> >
> >Btw., pedantic: shouldn't that be smp_mb()? Futexes don't operate on IO spaces, so
> >on UP they only need compiler barriers.
>
> Right, but we do in fact use smp barriers in this cases in the real code, that
> mb() is just in the comments, I guess it would be desirable to change it to
> smp_mb nonetheless.
>
> However, could these changes be in a followup? Mainly because the barrier B
> references will be updated across all futex.c... unless there are still concerns
> about this particular patch, of course.
How about doing it first in a preparatory patch? So that reviews of patches
actually making substantial changes don't get derailed by hard to read comments
and so.
Thanks,
Ingo
prev parent reply other threads:[~2016-02-06 8:22 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-04 6:28 [PATCH v5] futex: Remove requirement for lock_page in get_futex_key Davidlohr Bueso
2016-02-04 9:06 ` Thomas Gleixner
2016-02-04 17:43 ` Davidlohr Bueso
2016-02-04 17:50 ` Thomas Gleixner
2016-02-05 9:44 ` Ingo Molnar
2016-02-05 18:02 ` Davidlohr Bueso
2016-02-06 8:22 ` Ingo Molnar [this message]
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