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@xxxxxxxxxxxxx>
Signed-off-by: Mihai Carabas <mihai.carabas@xxxxxxxxxx>
---
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?
Give it a better name? Having ARCH_HAS_CPU_RELAX control a piece of code
that doesn't use cpu_relax() doesn't make sense to me.
The generic code for smp_cond_load_relaxed is using cpu_relax and this
one is used on x86 - so ARCH_HAS_CPU_RELAX is a prerequisite on x86 when
using haltpoll. Only on ARM64 this is overwritten. Moreover
ARCH_HAS_CPU_RELAX is controlling the function definition for
cpuidle_poll_state_init (this is how it was originally designed).
Thanks,
Mihai
