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Message-Id: <1232047618.8269.93.camel@think.oraclecorp.com>
Date: Thu, 15 Jan 2009 14:26:58 -0500
From: Chris Mason <chris.mason@...cle.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Ingo Molnar <mingo@...e.hu>, Matthew Wilcox <matthew@....cx>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Gregory Haskins <ghaskins@...ell.com>,
Andi Kleen <andi@...stfloor.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
linux-btrfs <linux-btrfs@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Nick Piggin <npiggin@...e.de>,
Peter Morreale <pmorreale@...ell.com>,
Sven Dietrich <SDietrich@...ell.com>,
Dmitry Adamushko <dmitry.adamushko@...il.com>,
Johannes Weiner <hannes@...xchg.org>
Subject: Re: [GIT PULL] adaptive spinning mutexes
On Thu, 2009-01-15 at 10:16 -0800, Linus Torvalds wrote:
>
> On Thu, 15 Jan 2009, Ingo Molnar wrote:
> >
> > btw., i think spin-mutexes have a design advantage here: in a lot of code
> > areas it's quite difficult to use spinlocks - cannot allocate memory,
> > cannot call any code that can sporadically block (but does not _normally_
> > block), etc.
> >
> > With mutexes those atomicity constraints go away - and the performance
> > profile should now be quite close to that of spinlocks as well.
>
> Umm. Except if you wrote the code nicely and used spinlocks, you wouldn't
> hold the lock over all those unnecessary and complex operations.
>
While this is true, there are examples of places we should expect
speedups for this today.
Concurrent file creation/deletion in a single dir will often find things
hot in cache and not have to block anywhere (mail spools).
Concurrent O_DIRECT aio writes to the same file, where i_mutex is
dropped early on.
pipes should see a huge improvement.
I'll kick off some runs of my three benchmarks on ext3 for comparison.
If there are things less synthetic people would like to see, please let
me know.
-chris
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