linux-ext4 - Re: [PATCH] jbd2: Use atomic variables to avoid taking t_handle_lock in jbd2_journal

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Message-ID: <20100803000609.GI25653@thunk.org>
Date:	Mon, 2 Aug 2010 20:06:09 -0400
From:	Ted Ts'o <tytso@....edu>
To:	john stultz <johnstul@...ibm.com>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Keith Maanthey <kmannth@...ibm.com>,
	Eric Whitney <eric.whitney@...com>
Subject: Re: [PATCH] jbd2: Use atomic variables to avoid taking
 t_handle_lock in jbd2_journal_stop

On Mon, Aug 02, 2010 at 04:02:32PM -0700, john stultz wrote:
> >From these numbers, it looks like the atomic variables are a minor
> improvement for -rt, but the improvement isn't as drastic as the earlier
> j_state lock change, or the vfs scalability patchset.

Thanks for doing this quick test run!  I was expecting to see a more
dramatic difference, since the j_state_lock patch removed one of the
two global locks in jbd2_journal_stop, and the t_handle_lock patch
removed the second of the two global locks.  But I guess the
j_state_lock contention in start_this_handle() is still the dominating factor.

It's interesting that apparently the latest t_handle_lock patch
doesn't seem to make much difference unless the VFS scalability patch
is also applied.  I'm not sure why that makes a difference, but it's
nice to know that with the VFS scalability patch it does seem to help,
even if it doesn't help as much as I had hoped.

OK, I guess we'll have to start working on the more aggressive
scalability fix ups....

						- Ted
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