linux-kernel - Re: multi-second application stall in open()

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Message-ID: <CAKA=qzZ_KhRbH6F4-TWvSAWiJyDsDrz4oUO5WppoMgWNEhyZmg@mail.gmail.com>
Date:	Tue, 26 Jun 2012 10:18:04 -0500
From:	Josh Hunt <joshhunt00@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: multi-second application stall in open()

On Tue, Jun 26, 2012 at 7:59 AM, Vivek Goyal <vgoyal@...hat.com> wrote:
> On Mon, Jun 25, 2012 at 11:01:48PM -0500, Josh Hunt wrote:
>
> [..]
>> So this really seems like a problem with kblockd not kicking in. I've
>> instrumented every path in select_queue and it's not getting hit after
>> schedule dispatch. Everything seems to stall at that point until a new
>> request comes in.
>
> Ok, that's cool. So now we need to find out why queued work is not being
> scheduled.
>
> I think there are some workqueue related trace points. If you enable those
> along with blktraces, that should give tejun some data to look at.
>
> Thanks
> Vivek

Tejun

Do you have any suggestions on how to debug this?

I did "perf record -a -e workqueue:*" and grabbed some tracepoint
data, but it's hard to correlate when these events are occurring in
the blktrace logs. Will keep investigating.
-- 
Josh
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