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Message-Id: <1232005443.14825.82.camel@laptop>
Date: Thu, 15 Jan 2009 08:44:03 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Nick Piggin <npiggin@...e.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Ingo Molnar <mingo@...e.hu>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Gregory Haskins <ghaskins@...ell.com>,
Matthew Wilcox <matthew@....cx>,
Andi Kleen <andi@...stfloor.org>,
Chris Mason <chris.mason@...cle.com>,
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>,
Peter Morreale <pmorreale@...ell.com>,
Sven Dietrich <SDietrich@...ell.com>,
Dmitry Adamushko <dmitry.adamushko@...il.com>,
Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH -v11][RFC] mutex: implement adaptive spinning
On Thu, 2009-01-15 at 01:46 +0100, Nick Piggin wrote:
> Hmm, well this is rather a slow path, I would say. I'd prefer not to
> modify schedule in this way (if we just get scheduled back on after
> being switched away, the subsequent call to schedule is going to be
> cache hot and not do too much work).
>
> preempt_enable_noresched maybe if you really care, would close up the
> window even more. But is it really worthwhile? We'd want to see numbers
> (when in doubt, keep it simpler).
I initially did the preempt_enable_no_resched() thing and that showed
some improvement for PREEMPT=y kernels (lost the numbers though).
When I redid all the patches I tried closing that last hole by doing
that __schedule() thing, never realizing that schedule() would then get
extra overhead,.. d'0h.
I agree that that isn't worth it. I shall revert to
preempt_enable_no_resched() and try to get some new numbers.
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