linux-kernel - Re: [PATCH 6/7] sched: Clean up preempt_enable_no

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Message-ID: <20131122113044.GL10022@twins.programming.kicks-ass.net>
Date:	Fri, 22 Nov 2013 12:30:44 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>
Cc:	Arjan van de Ven <arjan@...ux.intel.com>, lenb@...nel.org,
	rjw@...ysocki.net, Chris Leech <christopher.leech@...el.com>,
	David Miller <davem@...emloft.net>, rui.zhang@...el.com,
	jacob.jun.pan@...ux.intel.com,
	Mike Galbraith <bitbucket@...ine.de>,
	Ingo Molnar <mingo@...nel.org>, hpa@...or.com,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH 6/7] sched: Clean up preempt_enable_no_resched() abuse

On Fri, Nov 22, 2013 at 08:56:00AM +0200, Eliezer Tamir wrote:
> On 21/11/2013 15:39, Peter Zijlstra wrote:
> > On Thu, Nov 21, 2013 at 03:26:17PM +0200, Eliezer Tamir wrote:
> 
> >> We don't override any limit the user has put on the system call.
> > 
> > You are in fact, note how the normal select @endtime argument is only
> > set up _after_ you're done polling. So if the syscall had a timeout of 5
> > seconds, you just blew it by 55.
> > 
> 
> That's a bug, we will fix it.

The entire thing is a bug, and if I could take away sched_clock() from
you I would, but sadly its all inlines so I can't :-(

Please use local_clock(), yes its slightly more expensive, but I doubt
you can actually measure the effects on sane hardware.
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