Messages in this thread | | | Date | Sun, 28 Jan 2024 23:22:50 +0200 | Subject | Re: [PATCH 7/7] cpuidle/poll_state: replace cpu_relax with smp_cond_load_relaxed | From | Mihai Carabas <> |
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La 11.12.2023 13:46, Will Deacon a scris: > On Mon, Nov 20, 2023 at 04:01:38PM +0200, Mihai Carabas wrote: >> 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 | 14 +++++++++----- >> 1 file changed, 9 insertions(+), 5 deletions(-) >> >> diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c >> index 9b6d90a72601..440cd713e39a 100644 >> --- a/drivers/cpuidle/poll_state.c >> +++ b/drivers/cpuidle/poll_state.c >> @@ -26,12 +26,16 @@ 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; >> + >> + smp_cond_load_relaxed(¤t_thread_info()->flags, >> + (VAL & _TIF_NEED_RESCHED) || >> + (loop_count++ >= POLL_IDLE_RELAX_COUNT)); >> + >> + if (loop_count < POLL_IDLE_RELAX_COUNT) >> + break; >> + >> if (local_clock_noinstr() - time_start > limit) { >> dev->poll_time_limit = true; >> break; > Doesn't this make ARCH_HAS_CPU_RELAX a complete misnomer?
This controls the build of poll_state.c and the generic definition of smp_cond_load_relaxed (used by x86) is using cpu_relax(). Do you propose other approach here?
> > Will
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