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a=cvBusfyB2V15izCimMoJ:22 cc=ntf awl=host:12109 X-Proofpoint-ORIG-GUID: CgbJNDc1AXiLPQB9A9zO4awdpMKj85Wf Rafael J. Wysocki writes: > On Mon, Dec 15, 2025 at 5:55=E2=80=AFAM Ankur Arora wrote: >> >> The inner loop in poll_idle() polls over the thread_info flags, >> waiting to see if the thread has TIF_NEED_RESCHED set. The loop >> exits once the condition is met, or if the poll time limit has >> been exceeded. >> >> To minimize the number of instructions executed in each iteration, >> the time check is rate-limited. In addition, each loop iteration >> executes cpu_relax() which on certain platforms provides a hint to >> the pipeline that the loop busy-waits, allowing the processor to >> reduce power consumption. >> >> Switch over to tif_need_resched_relaxed_wait() instead, since that >> provides exactly that. >> >> However, given that when running in idle we want to minimize our power >> consumption, continue to depend on CONFIG_ARCH_HAS_CPU_RELAX as that >> serves as an indicator that the platform supports an optimized version >> of tif_need_resched_relaxed_wait() (via >> smp_cond_load_acquire_timeout()). >> >> Cc: "Rafael J. Wysocki" >> Cc: Daniel Lezcano >> Cc: linux-pm@vger.kernel.org >> Suggested-by: "Rafael J. Wysocki" >> Signed-off-by: Ankur Arora >> --- >> >> Notes: >> - use tif_need_resched_relaxed_wait() instead of >> smp_cond_load_relaxed_timeout() >> >> drivers/cpuidle/poll_state.c | 27 +++++---------------------- >> 1 file changed, 5 insertions(+), 22 deletions(-) >> >> diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c >> index c7524e4c522a..20136b3a08c2 100644 >> --- a/drivers/cpuidle/poll_state.c >> +++ b/drivers/cpuidle/poll_state.c >> @@ -6,41 +6,24 @@ >> #include >> #include >> #include >> -#include >> -#include >> #include >> #include >> #include >> >> -#define POLL_IDLE_RELAX_COUNT 200 >> - >> static int __cpuidle poll_idle(struct cpuidle_device *dev, >> struct cpuidle_driver *drv, int index) >> { >> - u64 time_start; >> - >> - time_start =3D local_clock_noinstr(); >> - >> dev->poll_time_limit =3D false; >> >> raw_local_irq_enable(); >> if (!current_set_polling_and_test()) { >> - unsigned int loop_count =3D 0; >> - u64 limit; >> + s64 limit; >> + bool nr_set; > > It doesn't look like the nr_set variable is really needed. > >> >> - limit =3D cpuidle_poll_time(drv, dev); >> + limit =3D (s64)cpuidle_poll_time(drv, dev); > > Is the explicit cast needed to suppress a warning? If not, I'd drop it. Ack. >> >> - while (!need_resched()) { >> - cpu_relax(); >> - if (loop_count++ < POLL_IDLE_RELAX_COUNT) >> - continue; >> - >> - loop_count =3D 0; >> - if (local_clock_noinstr() - time_start > limit) = { >> - dev->poll_time_limit =3D true; >> - break; >> - } >> - } >> + nr_set =3D tif_need_resched_relaxed_wait(limit); >> + dev->poll_time_limit =3D !nr_set; > > This can be > > dev->poll_time_limit =3D !tif_need_resched_relaxed_wait(limit); Yeah that looks pretty clear. Thanks! -- ankur