[PATCH 3/4] powerpc/64: context switch an hwsync instruction can be avoided

[Peter Zijlstra]

On Fri, Jun 09, 2017 at 01:36:08AM +1000, Nicholas Piggin wrote:
> The hwsync in the context switch code to prevent MMIO access being
> reordered from the point of view of a single process if it gets
> migrated to a different CPU is not required because there is an hwsync
> performed earlier in the context switch path.
> 
> Comment this so it's clear enough if anything changes on the scheduler
> or the powerpc sides. Remove the hwsync from _switch.
> 
> This improves context switch performance by 2-3% on POWER8.
> 
> Cc: Peter Zijlstra <peterz at infradead.org>
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>

Acked-by: Peter Zijlstra (Intel) <peterz at infradead.org>