linux-kernel - Re: schedule_delayed_work with a 0 jiffy delay

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Message-ID: <20140928142714.GB3736@mtj.dyndns.org>
Date:	Sun, 28 Sep 2014 10:27:14 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Joe Lawrence <joe.lawrence@...atus.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: schedule_delayed_work with a 0 jiffy delay

Hello, Joe.

On Fri, Sep 26, 2014 at 10:52:27AM -0400, Joe Lawrence wrote:
...
> I was wondering if such behavior was expected on !PREEMPT kernels,
> especially after b22ce2785d97 "workqueue: cond_resched() after
> processing each work item".  In the ftraces I've observed from the RCU
> stall, cond_resched() never seems to schedule.  Under what conditions
> would it be expected to do so?

Hmmm... it should yield if there's a higher priority task scheduled.
Maybe the workqueue in question is a highpri one?

> Changing the worker function to reschedule with at least 1 jiffy avoids
> this problem -- I was just curious if a fix at that end was appropriate.

The fact that 0 delay means immediate execution is depended upon in
multiple places and changing it will break other things.  The
workqueue user itself sounds buggy to me.  Can't that be fixed?

Thanks.

-- 
tejun
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