Re: [PATCH V2 0/6][RFC] futex: FUTEX_LOCK with optional adaptivespinning

From: Alan Cox
Date: Tue Apr 06 2010 - 09:49:31 EST

On Tue, 06 Apr 2010 15:35:31 +0200
Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> On Tue, 2010-04-06 at 16:28 +0300, Avi Kivity wrote:
> >
> > Yes, but that's the best case for spinning. You could simply use a
> > userspace spinlock in this case.
> Userspace spinlocks are evil.. they should _never_ be used.

Thats a gross and inaccurate simplification. For the case Avi is talking
about spinning in userspace makes sense in a lot of environments. Once
you've got one thread pinned per cpu (or gang scheduling >-) ) there are
various environments where it makes complete and utter sense.
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