Re: [PATCH 3/3] cpuidle: powernv: Avoid a branch in the core snooze_loop() loop

[Nicholas Piggin <npiggin@gmail.com>]

On Tue,  4 Apr 2017 07:54:14 +1000
Anton Blanchard <anton@ozlabs.org> wrote:

> From: Anton Blanchard <anton@samba.org>
> 
> When in the snooze_loop() we want to take up the least amount of
> resources. On my version of gcc (6.3), we end up with an extra
> branch because it predicts snooze_timeout_en to be false, whereas it
> is almost always true.
> 
> Use likely() to avoid the branch and be a little nicer to the
> other non idle threads on the core.

Patches 2 and 3 look fine. Should they be replicated to cpuidle-pseries.c
as well?

Thanks,
Nick

> 
> Signed-off-by: Anton Blanchard <anton@samba.org>
> ---
>  drivers/cpuidle/cpuidle-powernv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
> index 8c991c254b95..251a60bfa8ee 100644
> --- a/drivers/cpuidle/cpuidle-powernv.c
> +++ b/drivers/cpuidle/cpuidle-powernv.c
> @@ -58,7 +58,7 @@ static int snooze_loop(struct cpuidle_device *dev,
>  	ppc64_runlatch_off();
>  	HMT_very_low();
>  	while (!need_resched()) {
> -		if (snooze_timeout_en && get_tb() > snooze_exit_time)
> +		if (likely(snooze_timeout_en) && get_tb() > snooze_exit_time)
>  			break;
>  	}
>