linux-kernel - Re: Filesystem lockup with CONFIG_PREEMPT

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Message-ID: <1403926333.5113.12.camel@marge.simpson.net>
Date:	Sat, 28 Jun 2014 05:32:13 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Austin Schuh <austin@...oton-tech.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Richard Weinberger <richard.weinberger@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	rt-users <linux-rt-users@...r.kernel.org>
Subject: Re: Filesystem lockup with CONFIG_PREEMPT_RT

On Fri, 2014-06-27 at 18:18 -0700, Austin Schuh wrote:

> It would be more context switches, but I wonder if we could kick the
> workqueue logic completely out of the scheduler into a thread.  Have
> the scheduler increment/decrement an atomic pool counter, and wake up
> the monitoring thread to spawn new threads when needed?  That would
> get rid of the recursive pool lock problem, and should reduce
> scheduler latency if we would need to spawn a new thread.

I was wondering the same thing, and not only for workqueue, but also the
plug pulling.  It's kind of a wart to have that stuff sitting in the
hear of the scheduler in the first place, would be nice if it just went
away.  When a task can't help itself, you _could_ wake a proxy do that
for you.  Trouble is, I can imagine that being a heck of a lot of
context switches with some loads.. and who's gonna help the helper when
he blocks while trying to help?

-Mike

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