From: Nick Piggin <npiggin@kernel.dk>
Date: Tue, 17 Aug 2010 18:37:33 +0000 (+1000)
Subject: fs: fs_struct rwlock to spinlock
X-Git-Tag: v2.6.36-rc2~38^2~6
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2a4419b5b2a77f3f4537c14f7ad7df95770655dd;p=pandora-kernel.git

fs: fs_struct rwlock to spinlock

fs: fs_struct rwlock to spinlock

struct fs_struct.lock is an rwlock with the read-side used to protect root and
pwd members while taking references to them. Taking a reference to a path
typically requires just 2 atomic ops, so the critical section is very small.
Parallel read-side operations would have cacheline contention on the lock, the
dentry, and the vfsmount cachelines, so the rwlock is unlikely to ever give a
real parallelism increase.

Replace it with a spinlock to avoid one or two atomic operations in typical
path lookup fastpath.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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