linux-kernel - Re: [patch] sched: fix/add missing update_rq

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Message-ID: <20091112113429.GA7440@elte.hu>
Date:	Thu, 12 Nov 2009 12:34:29 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mike Galbraith <efault@....de>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch] sched: fix/add missing update_rq_clock() calls


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Thu, 2009-11-12 at 12:27 +0100, Ingo Molnar wrote:
> > * Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > On Thu, 2009-11-12 at 11:07 +0100, Mike Galbraith wrote:
> > > > sched: fix/add missing update_rq_clock() calls.
> > > > 
> > > > kthread_bind(), migrate_task() and sched_fork were missing updates, and
> > > > try_to_wake_up() was updating after having already used the stale clock.
> > > 
> > > 
> > > I'm almost at the point where I think we should ditch rq->clock 
> > > alltogether and simply call cpu_clock() directly when we need it. This 
> > > trying to optimize and avoid calling it game has brought way too many 
> > > head-aches.
> > 
> > It's not just about optimization - it's also accounting precision - we 
> > want to handle the full act of schedule() at a single timestamp - not a 
> > series of timestamps.
> > 
> > But ... we can get rid of it if it can be done sanely.
> 
> Ah, good point, hard to do for the migration paths though.

yes, migration is always the odd one out anyway, unless the hardware 
does cross-CPU-synchronous timestamps.

	Ingo
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