Subject: Re: [patch 2/2] powerpc: optimise smp_wmb

From: Benjamin Herrenschmidt <[email-masked]>
Date: Wed, 21 May 2008 11:43:00 -0400

On Wed, 2008-05-21 at 17:34 +0200, Nick Piggin wrote:
> On Wed, May 21, 2008 at 11:26:32AM -0400, Benjamin Herrenschmidt wrote:
> > 
> > On Wed, 2008-05-21 at 16:12 +0200, Nick Piggin wrote:
> > > lwsync is the recommended method of store/store ordering on caching enabled
> > > memory. For those subarchs which have lwsync, use it rather than eieio for
> > > smp_wmb.
> > 
> > Yuck... existence of lwsync depends on the processor at boot time...
> 
> Not according to the __stringify(LWSYNC) that I just removed. At least,
> presumably it is always present on 64 bit processors, and 32 bit ones
> will be no worse off as they'll continue just using eieio.

No, it doesn't exist on power3, but it degrades into a sync

Ben.