Re: [PATCH] xen: Send spinlock IPI to all waiters

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Fri, Feb 15, 2013 at 11:31:23AM +0000, Ian Campbell wrote:
> On Fri, 2013-02-15 at 11:26 +0000, Jan Beulich wrote:
> > >>> On 15.02.13 at 12:10, Ian Campbell <Ian.Campbell@citrix.com> wrote:
> > > On Fri, 2013-02-15 at 10:52 +0000, Stefan Bader wrote:
> > >> diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
> > >> index 83e866d..f7a080e 100644
> > >> --- a/arch/x86/xen/spinlock.c
> > >> +++ b/arch/x86/xen/spinlock.c
> > >> @@ -328,7 +328,6 @@ static noinline void xen_spin_unlock_slow(struct 
> > > xen_spinlock *xl)
> > >>  		if (per_cpu(lock_spinners, cpu) == xl) {
> > >>  			ADD_STATS(released_slow_kicked, 1);
> > >>  			xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
> > >> -			break;
> > > 
> > > It would be more efficient to build a mask and use xen_send_IPI_mask().
> > 
> > In order for __xen_send_IPI_mask() to then take the list apart
> > again and call xen_send_IPI_one()? There's no batching
> > implemented currently...
> 
> Oh, I simply assumed it must obviously do that!

Perhaps if it was done via a multicall? We could batch then things up. But I recall
you saying that for homogeneous calls it is silly to use multicalls.

> 
> Ian.
>