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

[Ian Campbell <ian.campbell@citrix.com>]

On Tue, 2015-09-15 at 11:39 +0100, Stefano Stabellini wrote:
> On Tue, 15 Sep 2015, Ian Campbell wrote:
> > On Mon, 2015-08-03 at 12:29 +0100, Ian Campbell wrote:
> > > From: David Vrabel <david.vrabel@citrix.com>
> > > 
> > > 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.
> > > 
> > > For consistency also move arch_lock_(acquire|release)_barrier to
> > > asm/spinlock.h.
> > > 
> > > Booted the result on arm32 (Midway) and arm64 (Mustang). Build test
> > > only on amd64.
> > > 
> > > Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> > > [ijc: add barrier, rename as arch_lock_*, move arch_lock_*_barrier,
> > > test]
> > > Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> > > Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> > > Cc: Jan Beulich <jbeulich@suse.com>
> > > Cc: Andrew Cooper <andrew.cooper3@citrix.com>
> > 
> > Andy has Reviewed-by but this change still lacks an Ack from the ARM
> > side.
> > Stefano, was your previous "The code should work though." intended as
> > an
> > Ack?
> 
> Yes

Applied then. thanks.

Ian.