linux-kernel - Re: [REPORT] cfs-v4 vs sd-0.44

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Date:	Mon, 23 Apr 2007 10:07:20 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ulrich Drepper <drepper@...il.com>
Cc:	William Lee Irwin III <wli@...omorphy.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kyle Moffett <mrmacman_g4@....com>, Willy Tarreau <w@....eu>,
	Ingo Molnar <mingo@...e.hu>, Con Kolivas <kernel@...ivas.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Williams <pwil3058@...pond.net.au>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr,
	Gene Heskett <gene.heskett@...il.com>
Subject: Re: [REPORT] cfs-v4 vs sd-0.44

On Sun, 2007-04-22 at 09:16 -0700, Ulrich Drepper wrote:
> On 4/22/07, William Lee Irwin III <wli@...omorphy.com> wrote:
> > On Sun, Apr 22, 2007 at 12:17:31AM -0700, Ulrich Drepper wrote:
> > > For futex(), the extension is needed for the FUTEX_WAIT operation.  We
> > > need a new operation FUTEX_WAIT_FOR or so which takes another (the
> > > fourth) parameter which is the PID of the target.
> > > For FUTEX_LOCK_PI we need no extension.  The futex value is the PID of
> > > the current owner.  This is required for the whole interface to work
> > > in the first place.
> >
> > We'll have to send things out and see what sticks here. There seems to
> > be some pickiness above.
> 
> I know Rusty will shudder since it makes futexes yet more complicated
> (although only if the user wants it) but if you introduce the concept
> of "yield to" then this extension makes really sense and it is a quite
> simple extension.  Plus: I'm the most affected by the change since I
> have to change code to use it and I'm fine with it.

Hi Uli,

	I wouldn't worry: futexes long ago jumped the shark.

	I think it was inevitable that once we started endorsing programs
bypassing the kernel for IPC that we'd want some form of yield_to().
And yield_to(p) has much more sane semantics than yield().

Cheers,
Rusty.


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