linux-kernel - Re: [patch 00/52] vfs scalability patches updated

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Date:	Fri, 2 Jul 2010 03:23:17 +1000
From:	Nick Piggin <npiggin@...e.de>
To:	Dave Chinner <david@...morbit.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	John Stultz <johnstul@...ibm.com>,
	Frank Mayhar <fmayhar@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch 00/52] vfs scalability patches updated

On Wed, Jun 30, 2010 at 10:40:49PM +1000, Nick Piggin wrote:
> But actually it's not all for scalability. I have some follow on patches
> (that require RCU inodes, among other things) that actually improve
> single threaded performance significnatly. git diff workload IIRC was
> several % improved from speeding up stat(2).

I rewrote the store-free path walk patch that goes on top of this
patchset (it's now much cleaner and more optimised, I'll post a patch
soonish). It is quicker than I remembered.

A single thread running stat(2) in a loop on a file "./file" has the
following cost (on an 2s8c Barcelona):

2.6.35-rc3	595 ns/op
patched		336 ns/op

stat(2) takes 56% the time with patches. It's something like 13 fewer
atomic operations per syscall.

What's that good for? A single threaded, cached `git diff` on the linux
kernel tree takes just 81% of the time after the vfs patches (0.27s vs
0.33s).

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