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    SubjectRE: [PATCH v4 7/8] cpuidle/poll_state: replace cpu_relax with smp_cond_load_relaxed
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    Tomohiro Misono (Fujitsu) <misono.tomohiro@fujitsu.com> writes:

    > Hi,
    > > Subject: [PATCH v4 7/8] cpuidle/poll_state: replace cpu_relax with smp_cond_load_relaxed
    > >
    > > cpu_relax on ARM64 does a simple "yield". Thus we replace it with
    > > smp_cond_load_relaxed which basically does a "wfe".
    > >
    > > Suggested-by: Peter Zijlstra <peterz@infradead.org>
    > > Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
    > > ---
    > > drivers/cpuidle/poll_state.c | 15 ++++++++++-----
    > > 1 file changed, 10 insertions(+), 5 deletions(-)
    > >
    > > diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
    > > index 9b6d90a72601..1e45be906e72 100644
    > > --- a/drivers/cpuidle/poll_state.c
    > > +++ b/drivers/cpuidle/poll_state.c
    > > @@ -13,6 +13,7 @@
    > > static int __cpuidle poll_idle(struct cpuidle_device *dev,
    > > struct cpuidle_driver *drv, int index)
    > > {
    > > + unsigned long ret;
    > > u64 time_start;
    > >
    > > time_start = local_clock_noinstr();
    > > @@ -26,12 +27,16 @@ static int __cpuidle poll_idle(struct cpuidle_device *dev,
    > >
    > > limit = cpuidle_poll_time(drv, dev);
    > >
    > > - while (!need_resched()) {
    > > - cpu_relax();
    > > - if (loop_count++ < POLL_IDLE_RELAX_COUNT)
    > > - continue;
    > > -
    > > + for (;;) {
    > > loop_count = 0;
    > > +
    > > + ret = smp_cond_load_relaxed(&current_thread_info()->flags,
    > > + VAL & _TIF_NEED_RESCHED ||
    > > + loop_count++ >= POLL_IDLE_RELAX_COUNT);
    > > +
    > > + if (!(ret & _TIF_NEED_RESCHED))
    > > + break;
    >
    > Should this be "if (ret & _TIF_NEED_RESCHED) since we want to break here
    > if the flag is set, or am I misunderstood?

    Yeah, you are right. The check is inverted.

    I'll be re-spinning this series. Will fix. Though, it probably makes sense
    to just keep the original "while (!need_resched())" check.

    Thanks for the review.

    --
    ankur

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