linux-kernel - Re: [RFC 3/4] Disable scheduler tick when we are running SCHED

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Message-ID: <20100908142826.GI7436@bolzano.suse.de>
Date:	Wed, 8 Sep 2010 16:28:26 +0200
From:	Jan Blunck <jblunck@...ell.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linux-Kernel Mailinglist <linux-kernel@...r.kernel.org>,
	linux-rt-users@...r.kernel.org,
	Sven-Thorsten Dietrich <sdietrich@...ell.com>,
	Michael Galbraith <MGalbraith@...ell.com>
Subject: Re: [RFC 3/4] Disable scheduler tick when we are running
	SCHED_FIFO tasks

On Wed, Sep 08, Peter Zijlstra wrote:

> On Wed, 2010-09-08 at 14:29 +0200, Jan Blunck wrote:
> > This patch is disabling the scheduler tick to go off when there is a task
> > with SCHED_FIFO policy running. Since these tasks are not timesliced anyway
> > we only care about timers, softirqs and such stuff just like when we disable
> > the tick during idle periods.
> > 
> 
> Also, doesn't this break any and all jiffies users?
> 

Sure. It was enough to make FTQ run.

> And you need to restart the tick on call_rcu() and everything else that
> requires the tick for processing.
> 

I realized that before as well but somehow forgot about it. Checking for a
disabled timer tick on syscall entry would help. Like we do on irq entry as
well.

Jan
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