Re: [PATCH] cpuidle: arm: make enter idle operation a bit more efficient

Lorenzo Pieralisi
2016-03-24T16:03:42Z

On Thu, Mar 24, 2016 at 01:07:18PM +0800, Jisheng Zhang wrote:
> Currently, entering idle need to check the idx every time to choose the
> real entering idle routine. But this check could be avoided by pointing
> the idle enter function pointer of each idle states to the routines
> suitable for each states directly.
>
> Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
> ---
> drivers/cpuidle/cpuidle-arm.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/cpuidle/cpuidle-arm.c b/drivers/cpuidle/cpuidle-arm.c
> index 545069d..48a620f 100644
> --- a/drivers/cpuidle/cpuidle-arm.c
> +++ b/drivers/cpuidle/cpuidle-arm.c
> @@ -23,6 +23,13 @@
>
> #include "dt_idle_states.h"
>
> +static int arm_enter_wfi_state(struct cpuidle_device *dev,
> + struct cpuidle_driver *drv, int idx)
> +{
> + cpu_do_idle();
> + return 0;
> +}
> +
> /*
> * arm_enter_idle_state - Programs CPU to enter the specified state
> *
> @@ -38,11 +45,6 @@ static int arm_enter_idle_state(struct cpuidle_device *dev,
> {
> int ret;
>
> - if (!idx) {
> - cpu_do_idle();
> - return idx;
> - }

Mmm...if I wanted to paint your bikeshed I would say idx is in a
register and you are removing a simple comparison to exchange it
with a function that adds to code footprint and may even make
performance worse instead of improving anything.

I am not sure this patch makes anything more efficient, happy to be
proven wrong, with significant data.

Thanks,
Lorenzo

> -
> ret = cpu_pm_enter();
> if (!ret) {
> /*
> @@ -69,7 +71,7 @@ static struct cpuidle_driver arm_idle_driver = {
> * handler for idle state index 0.
> */
> .states[0] = {
> - .enter = arm_enter_idle_state,
> + .enter = arm_enter_wfi_state,
> .exit_latency = 1,
> .target_residency = 1,
> .power_usage = UINT_MAX,
> --
> 2.8.0.rc3
>