Re: [patch 04/15] Generic Mutex Subsystem, add-atomic-call-func-x86_64.patch

[Nicolas Pitre <nico@cam.org>]

On Tue, 20 Dec 2005, Nick Piggin wrote:

> Nicolas Pitre wrote:
> > On Tue, 20 Dec 2005, Ingo Molnar wrote:
> > 
> > 
> > > * David Woodhouse <dwmw2@infradead.org> wrote:
> > > 
> > > 
> > > > On Mon, 2005-12-19 at 09:49 -0800, Zwane Mwaikambo wrote:
> > > > 
> > > > > Hi Ingo,
> > > > >        Doesn't this corrupt caller saved registers?
> > > > 
> > > > Looks like it. I _really_ don't like calling functions from inline asm.
> > > > It's not nice. Can't we use atomic_dec_return() for this?
> > > 
> > > we can use atomic_dec_return(), but that will add one more instruction to
> > > the fastpath. OTOH, atomic_dec_return() is available on every
> > > architecture, so it's a really tempting thing. I'll experiment with it.
> > 
> > 
> > Please consider using (a variant of) xchg() instead.  Although atomic_dec()
> > is available on all architectures, its implementation is far from being the
> > most efficient thing to do for them all.  For example, see my discussion
> > about swp on ARM:
> > 
> 
> Considering that on UP, the arm should not need to disable interrupts
> for this function (or has someone refuted Linus?), how about:

Kernel preemption.


Nicolas
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