Re: [Xen-devel] [PATCH v2] arm: reduce power use by contented spin locks with WFE/SEV

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2015-08-11 at 09:07 -0600, Jan Beulich wrote:
> > > > On 03.08.15 at 13:29, <ian.campbell@xxxxxxxxxx> wrote:
> > From: David Vrabel <david.vrabel@xxxxxxxxxx>
> > 
> > Instead of cpu_relax() while spinning and observing the ticket head,
> > introduce arch_lock_relax() which executes a WFE instruction.  After
> > the ticket head is changed call arch_lock_signal() to execute an SEV
> > instruction (with the required DSB first) to wake any spinners.
> > 
> > This should improve power consumption when locks are contented and
> > spinning.
> 
> So why not use MONITOR/MWAIT on x86 for the same purpose?

I'll leave this for an x86 person to decide/implement.

Ian.

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