linux-kernel - Re: Announce: Semaphore-Removal tree

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Message-ID: <20080426093048.GA11443@infradead.org>
Date:	Sat, 26 Apr 2008 05:30:48 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Daniel Walker <dwalker@...sta.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Matthew Wilcox <matthew@....cx>, linux-kernel@...r.kernel.org,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: Announce: Semaphore-Removal tree

On Fri, Apr 25, 2008 at 02:22:31PM -0700, Daniel Walker wrote:
> If you can make a case for converting some semaphores to spinlocks be my
> guest .. If you have good reasoning I wouldn't stand in the way.. (Real
> time converts all the spinlocks to mutexes anyway ..)

Right at hand I have the XFS inode hash lock was converted from a rw_semaphore
to a rwlock_t becuase the context switch overhead was killing
performance in various benchmarks. This is a very typical scenary for
locks that are taken often and held for a rather short time.  Add to
that fact that a spinlock is compltely optimized away for an UP kernel
while a mutex is not and the amount of memory that any mutex takes
compared to a spinlock you have a clear winner.

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