Re: [PATCH] Enable haltpoll for arm64

[Mihai Carabas]

> Using poll_state as is on arm64 seems sub-optimal, would not something
> like the below make sense?
>
> ---
> diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
> index 9b6d90a72601..9ab40198b042 100644
> --- a/drivers/cpuidle/poll_state.c
> +++ b/drivers/cpuidle/poll_state.c
> @@ -27,7 +27,11 @@ static int __cpuidle poll_idle(struct cpuidle_device *dev,
>   		limit = cpuidle_poll_time(drv, dev);
>   
>   		while (!need_resched()) {
> -			cpu_relax();
> +
> +			smp_cond_load_relaxed(current_thread_info()->flags,
> +					      (VAL & TIF_NEED_RESCHED) ||
> +					      (loop_count++ >= POLL_IDLE_RELAX_COUNT));
> +
>   			if (loop_count++ < POLL_IDLE_RELAX_COUNT)
>   				continue;
>   

Thank you for the suggestion. I have tried it and also different 
variations like [1] to respect the initial logic
but I obtain poor performance compared to the initial one:

perf bench sched pipe
# Running 'sched/pipe' benchmark:
# Executed 1000000 pipe operations between two processes

     Total time: 136.215 [sec]

     136.215229 usecs/op
           7341 ops/sec


[1]

--- 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(&current_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;