From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Brian Foster <bfoster@redhat.com>, linux-xfs@vger.kernel.org
Subject: Re: [PATCH for-4.14] xfs: fix AIM7 regression
Date: Thu, 19 Oct 2017 15:44:31 -0700 [thread overview]
Message-ID: <20171019224431.GO4755@magnolia> (raw)
In-Reply-To: <20171019131407.GA20645@lst.de>
On Thu, Oct 19, 2017 at 03:14:07PM +0200, Christoph Hellwig wrote:
> On Thu, Oct 19, 2017 at 07:38:48AM -0400, Brian Foster wrote:
> > On Thu, Oct 19, 2017 at 09:47:05AM +0200, Christoph Hellwig wrote:
> > > Apparently our current rwsem code doesn't like doing the trylock, then
> > > lock for real scheme. So change our read/write methods to just do the
> > > trylock for the RWF_NOWAIT case. This fixes a ~25% regression in
> > > AIM7.
> > >
> >
> > The code looks fine, but this seems really strange. If the trylock
> > fails, then wouldn't the blocking lock have slept anyways if done
> > initially? Is there any more background info available on this, or
> > perhaps a theory on why there is such a significant regression..?
>
> No, unfortunately I don't have a theory, but I agree it is odd
> behavior in the rwsem code.
<shrug> I want to know a little more about why there's a performance hit
in the down_read_trylock -> down_read case. Are we getting penalized
for that? Is it some weird interaction with lockdep?
--D
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next prev parent reply other threads:[~2017-10-19 22:44 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-19 7:47 [PATCH for-4.14] xfs: fix AIM7 regression Christoph Hellwig
2017-10-19 11:38 ` Brian Foster
2017-10-19 13:14 ` Christoph Hellwig
2017-10-19 22:44 ` Darrick J. Wong [this message]
2017-10-20 6:55 ` Christoph Hellwig
2017-11-07 10:22 ` Jan Kara
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