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Re: xfs-trace-ilock-more

To: Mark Fasheh <mfasheh@xxxxxxx>
Subject: Re: xfs-trace-ilock-more
From: Jeff Mahoney <jeffm@xxxxxxxx>
Date: Wed, 14 Dec 2011 14:24:32 -0500
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20111214182750.GH11114@xxxxxxxxxxxxx>
References: <20111214024040.GA17780@xxxxxxxxxxxxx> <20111214182750.GH11114@xxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:7.0.1) Gecko/20110929 Thunderbird/7.0.1
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On 12/14/2011 01:27 PM, Mark Fasheh wrote:
> Hey Christoph,
> 
> On Tue, Dec 13, 2011 at 09:40:40PM -0500, Christoph Hellwig wrote:
>> Can you explain the story behid this patch in SLES11SP1?
> 
> We were looking at some performance issues and needed a bit more
> information on the amount of time spent in ilock. I can give you
> more specifics if you want, I just have to dig up the e-mails (it's
> been a while).

That's pretty much the explanation. With heavy reader load, buffered
writes were stalling for 80 ms and sometimes longer. I suspected it
was contention on the ilock and the tracing with that patch
demonstrated a delay there. Since we were chasing a similar issue at
another site, it seemed worthwhile to just keep it around. We're still
tracking down the cause. I'm not sure if more recent kernels have the
same issue as there's been quite a lot of churn.

- -Jeff

- -- 
Jeff Mahoney
SUSE Labs
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