linux-kernel - Re: [patch] change futex

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Message-ID: <20070312110417.GA12308@elte.hu>
Date:	Mon, 12 Mar 2007 12:04:17 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Roland McGrath <roland@...hat.com>, akpm@...ux-foundation.org,
	mm-commits@...r.kernel.org, npiggin@...e.de, drepper@...hat.com,
	oleg@...sign.ru, sebastien.dugue@...l.net,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] change futex_wait() to hrtimers


* Andi Kleen <andi@...stfloor.org> wrote:

> On Mon, Mar 12, 2007 at 12:00:20PM +0100, Thomas Gleixner wrote:
> > On Mon, 2007-03-12 at 12:27 +0100, Andi Kleen wrote:
> > > Ingo Molnar <mingo@...e.hu> writes:
> > > > 
> > > > the only correct approach is the use of hrtimers, and a patch exists for 
> > > > that - see below. This has been included in -rt for quite some time.
> > > 
> > > But isn't that bad for power management? You'll likely get more
> > > idle wakeups, won't you?
> > 
> > Why so ? It comes more precise, but only once.
> 
> When it's clustered around the jiffies interval then wakeups from 
> multiple processes will be somewhat batched. With a precise wakeup 
> you'll get wakeups all over the jiffies period, won't you?

if HIGH_RES_TIMERS is disabled then that is what happens. But frankly, 
most futex waits are without timeouts - if an application cares about 
micro-effects like that then you are much better off not using a 
per-futex timeout anyway.

	Ingo
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