From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH -v9][RFC] mutex: implement adaptive spinning
Date: Wed, 14 Jan 2009 12:21:58 +0100
Message-ID: <20090114112158.GA8625@elte.hu>
References: <1231774622.4371.96.camel@laptop> <1231859742.442.128.camel@twins> <alpine.LFD.2.00.0901130812590.6528@localhost.localdomain> <1231863710.7141.3.camel@twins> <1231864854.7141.8.camel@twins> <alpine.LFD.2.00.0901130846320.6528@localhost.localdomain> <1231867314.7141.16.camel@twins> <1231901899.1709.18.camel@think.oraclecorp.com>
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Cc: Peter Zijlstra <peterz@infradead.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"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>
To: Chris Mason <chris.mason@oracle.com>
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In-Reply-To: <1231901899.1709.18.camel@think.oraclecorp.com>
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* Chris Mason <chris.mason@oracle.com> wrote:

> v10 is better that not spinning, but its in the 5-10% range.  So, I've 
> been trying to find ways to close the gap, just to understand exactly 
> where it is different.
> 
> If I take out:
> 	/*
> 	 * If there are pending waiters, join them.
> 	 */
> 	if (!list_empty(&lock->wait_list))
> 		break;
> 
> 
> v10 pops dbench 50 up to 1800MB/s.  The other tests soundly beat my 
> spinning and aren't less fair.  But clearly this isn't a good solution.

i think since we already decided that it's ok to be somewhat unfair (_all_ 
batching constructs introduce unfairness, so the question is never 'should 
we?' but 'by how much?'), we should just take this out and enjoy the speed 
...

	Ingo