On Thu, 2024-02-15 at 09:41 +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@xxxxxxxxxxxxx>
> Signed-off-by: Mihai Carabas <mihai.carabas@xxxxxxxxxx>
> ---
> 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);
Is it necessary to repeat this 200 times with a wfe poll? Does kvm not
implement a timeout period?
Could you make it configurable? This patch improves certain workloads
on AWS Graviton instances as well, but blocks up to 6ms in 200 * 30us
increments before going to wfi, which is a bit excessive.
> +
> + if (!(ret & _TIF_NEED_RESCHED))
> + break;
> +
> if (local_clock_noinstr() - time_start > limit) {
> dev->poll_time_limit = true;
> break;
