Re: [PATCH] cpuidle: menu: Optimize bucket assignment when next_timer_ns equals KTIME_MAX

[Zhongqiu Han]

On 4/3/2025 6:06 PM, Christian Loehle wrote:
> On 4/3/25 11:01, Zhongqiu Han wrote:
> > On 4/3/2025 5:34 PM, Christian Loehle wrote:
> > > On 4/3/25 10:28, Zhongqiu Han wrote:
> > > > Directly assign the last bucket value instead of calling which_bucket()
> > > > when next_timer_ns equals KTIME_MAX, the largest possible value that
> > > > always falls into the last bucket. This avoids unnecessary calculations
> > > > and enhances performance.
> > > >
> > > > Signed-off-by: Zhongqiu Han <quic_zhonhan@xxxxxxxxxxx>
> > >
> > > Reviewed-by: Christian Loehle <christian.loehle@xxxxxxx>
> > >
> > > > ---
> > > >    drivers/cpuidle/governors/menu.c | 7 ++++++-
> > > >    1 file changed, 6 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
> > > > index 39aa0aea61c6..8fc7fbed0052 100644
> > > > --- a/drivers/cpuidle/governors/menu.c
> > > > +++ b/drivers/cpuidle/governors/menu.c
> > > > @@ -255,7 +255,12 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
> > > >             */
> > > >            data->next_timer_ns = KTIME_MAX;
> > > >            delta_tick = TICK_NSEC / 2;
> > > > -        data->bucket = which_bucket(KTIME_MAX);
> > > > +        /*
> > > > +         * Assign the last bucket value directly instead of calling
> > > > +         * which_bucket(), since KTIME_MAX is the largest possible
> > > > +         * value that always falls into the last bucket.
> > > > +         */
> > >
> > > comment almost seems overkill.
> > >
> > > > +        data->bucket = BUCKETS - 1;
> > > >        }
> > > >          if (unlikely(drv->state_count <= 1 || latency_req == 0) ||
> > Thanks Christian for the review~
> >
> > Actually I just want to add a comment to indicate that which_bucket()
> > was once called here, in case which_bucket() changes in the future,
> > and however, we stayed with the original approach, leading to the
> > inconsistency.
> >
> > Could you please review the comment below and let me know if it's okay
> > or if I should not add any log? Thanks a lot~
> >
> > /* KTIME_MAX falls into the last bucket, skip which_bucket(). */
> >
> >
> >
> > I will collect review comments before arise patch V2.
>
> Honestly I'd be fine without a comment, it's pretty obvious that
> everything containing "bucket =" needs to be changed if the bucket
> logic ever changes.
Thanks Christian, let me wait more other aspects comments~

--
Thx and BRs,
Zhongqiu Han