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

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Message-ID: <20100913181925.GA15107@Krystal>
Date:	Mon, 13 Sep 2010 14:19:25 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Ingo Molnar <mingo@...e.hu>
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

* Ingo Molnar (mingo@...e.hu) wrote:
> 
> * 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 ...

Yep, that's fine with me.

Thanks!

Mathieu

> 
> Thanks,
> 
> 	Ingo

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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