Subject: Re: [PATCH -v8][RFC] mutex: implement adaptive spinning
From: Peter Zijlstra <peterz@infradead.org>
To: Chris Mason <chris.mason@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
       Ingo Molnar <mingo@elte.hu>,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       Gregory Haskins <ghaskins@novell.com>, Matthew Wilcox <matthew@wil.cx>,
       Andi Kleen <andi@firstfloor.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       linux-fsdevel <linux-fsdevel@vger.kernel.org>,
       linux-btrfs <linux-btrfs@vger.kernel.org>,
       Thomas Gleixner <tglx@linutronix.de>, Nick Piggin <npiggin@suse.de>,
       Peter Morreale <pmorreale@novell.com>,
       Sven Dietrich <SDietrich@novell.com>,
       Dmitry Adamushko <dmitry.adamushko@gmail.com>
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Date: Mon, 12 Jan 2009 17:50:15 +0100
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On Mon, 2009-01-12 at 11:45 -0500, Chris Mason wrote:
> On Mon, 2009-01-12 at 08:20 -0800, Linus Torvalds wrote:
> > 
> > On Mon, 12 Jan 2009, Linus Torvalds wrote:
> > > 
> > > You made it back into the locked version.
> > 
> > Btw, even if you probably had some reason for this, one thing to note is 
> > that I think Chris' performance testing showed that the version using a 
> > lock was inferior to his local btrfs hack, while the unlocked version 
> > actually beat his hack.
> > 
> 
> The spinning hack was faster than everything before v7 (we'll call it
> the Linus-fix), and the v7 code was much faster than my spin.
> 
> This is somewhere in between, with slightly better fairness than v7.
> 
>              spin         v7         v8
> dbench 50    580MB/s      789MB/s    421MB/s
> file creates 152 file/s   162 file/s 195 file/s
> file stat    3.8s total   2.3s total 5.3s total
> 
> (the file stat run is total run time, so lower is better.  The other
> numbers are files or MB per second, so higher is better)
> 
> For the file create run, v8 had much lower system time than v7,
> averaging 1s of sys time per proc instead of 1.6s.

Right, how about the spread in completion time, because that is the only
reason I tried this fairness stuff, because you reported massive
differences there.

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