Messages in this thread | | | From | Ankur Arora <> | Subject | RE: [PATCH v4 7/8] cpuidle/poll_state: replace cpu_relax with smp_cond_load_relaxed | Date | Tue, 27 Feb 2024 20:36:45 -0800 |
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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(¤t_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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