linux-kernel - Re: [RFC PATCH] check_preempt_tick should not compare vruntime with wall time

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Message-ID: <20100913180348.GA20171@elte.hu>
Date:	Mon, 13 Sep 2010 20:03:48 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tony Lindgren <tony@...mide.com>,
	Mike Galbraith <efault@....de>
Subject: Re: [RFC PATCH] check_preempt_tick should not compare vruntime with
 wall time


* Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> * Linus Torvalds (torvalds@...ux-foundation.org) wrote:
> > On Mon, Sep 13, 2010 at 9:16 AM, Mathieu Desnoyers
> > <mathieu.desnoyers@...icios.com> wrote:
> > >
> > > OK, the long IRC discussions we just had convinced me that the current scheme
> > > takes things into account by adapting the granularity dynamically, but also got
> > > me to notice that check_preempt seems to compare vruntime with wall time, which
> > > is utterly incorrect. So maybe all my patch was doing was to expose this bug:
> > 
> > Do you have latency numbers for this patch?
> 
> Sure, see below,
> 
> In addition to this patch, [...]

Note, which is a NOP for your latency workload.

> [...] I also used Peter's approach of reducing the minimum granularity

Ok, that's the very first patch i sent yesterday morning - so we also 
have my numbers that it reduces latencies.

To move things along i'll apply it with your Reported-by and Acked-by 
line, ok?

We can also work on the other, more complex things after that, but first 
lets make some progress on the latency front ...

Thanks,

	Ingo
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