linux-kernel - Re: [PATCH] fs-writeback: drop wb->list_lock during blk_finish

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Date:	Mon, 14 Sep 2015 08:56:50 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Chris Mason <clm@...com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Josef Bacik <jbacik@...com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Neil Brown <neilb@...e.de>, Jan Kara <jack@...e.cz>,
	Christoph Hellwig <hch@....de>
Subject: Re: [PATCH] fs-writeback: drop wb->list_lock during blk_finish_plug()

On Sun, Sep 13, 2015 at 09:12:44AM -0400, Chris Mason wrote:
> On Sat, Sep 12, 2015 at 07:46:32PM -0400, Chris Mason wrote:
> > I don't think the XFS numbers can be trusted too much since it was
> > basically bottlenecked behind that single pegged CPU.  It was bouncing
> > around and I couldn't quite track it down to a process name (or perf
> > profile).
> 
> I'll do more runs Monday, but I was able to grab a perf profile of the
> pegged XFS CPU.  It was just the writeback worker thread, and it
> hit btrfs differently because we defer more of this stuff to endio
> workers, effectively spreading it out over more CPUs.
> 
> With 4 mount points intead of 2, XFS goes from 140K files/sec to 250K.
> Here's one of the profiles, but it bounced around a lot so I wouldn't
> use this to actually tune anything:

mkfs.xfs -d agcount=64 ....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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