Re: [PATCH 06/14] powerpc/64s: interrupt replay balance the return branch predictor

[Nicholas Piggin <npiggin@gmail.com>]

On Tue, 13 Jun 2017 19:51:19 +1000
Michael Ellerman <mpe@ellerman.id.au> wrote:

> Nicholas Piggin <npiggin@gmail.com> writes:
> 
> > The __replay_interrupt code is branched to with bl, but the caller is
> > returned to directly with rfid from the interrupt.
> >
> > Instead return to a return stub that returns to the caller with blr,
> > which should do better with the return predictor.
> >
> > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> > ---
> >  arch/powerpc/kernel/exceptions-64s.S | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
> > index a04ee0d7f88e..d55201625ea3 100644
> > --- a/arch/powerpc/kernel/exceptions-64s.S
> > +++ b/arch/powerpc/kernel/exceptions-64s.S
> > @@ -1586,7 +1586,7 @@ _GLOBAL(__replay_interrupt)
> >  	 * we don't give a damn about, so we don't bother storing them.
> >  	 */
> >  	mfmsr	r12
> > -	mflr	r11
> > +	LOAD_REG_ADDR(r11, __replay_interrupt_return)  
> 
> Can you make it a local label, to make it clear nothing outside the file
> returns to there, and to not clutter the symbol map?

I can do that. Interrupt returns will now get significantly
attributed to this guy in profiles (and you can see it on some
sleep/wake workloads). __replay_interrupt is probably better
than arch_local_irq_restore, I guess.

Thanks,
Nick