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

Jisheng Zhang
2016-03-25T06:32:03Z

Hi Lorenzo,

On Thu, 24 Mar 2016 16:06:00 +0000 Lorenzo Pieralisi wrote:

> 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 for pointing this out. I'll do some measurement and get back to you

Thanks,
Jisheng