[5/5] cpuidle: implement poll_idle() using smp_vcond_load_relaxed()

Commit Message

Haris Okanovic Nov. 5, 2024, 6:30 p.m. UTC

Implement poll_idle() using smp_vcond_load_relaxed() function.

Signed-off-by: Haris Okanovic <[e-mail]>
---
 drivers/cpuidle/poll_state.c | 36 +++++-------------------------------
 1 file changed, 5 insertions(+), 31 deletions(-)

Comments

Christoph Lameter (Ampere) Nov. 5, 2024, 7:45 p.m. UTC | #1

On Tue, 5 Nov 2024, Haris Okanovic wrote:

>  {
> -	u64 time_start;
> -
> -	time_start = local_clock_noinstr();
> +	unsigned long flags;

Lets keep recording that start value here. Otherwise the timeout could me
later than expected.

Patch

diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
index 61df2395585e..5553e6f31702 100644
--- a/drivers/cpuidle/poll_state.c
+++ b/drivers/cpuidle/poll_state.c
@@ -7,46 +7,20 @@ 
 #include <linux/sched.h>
 #include <linux/sched/clock.h>
 #include <linux/sched/idle.h>
-
-#ifdef CONFIG_ARM64
-/*
- * POLL_IDLE_RELAX_COUNT determines how often we check for timeout
- * while polling for TIF_NEED_RESCHED in thread_info->flags.
- *
- * Set this to a low value since arm64, instead of polling, uses a
- * event based mechanism.
- */
-#define POLL_IDLE_RELAX_COUNT	1
-#else
-#define POLL_IDLE_RELAX_COUNT	200
-#endif
+#include <asm/barrier.h>
 
 static int __cpuidle poll_idle(struct cpuidle_device *dev,
 			       struct cpuidle_driver *drv, int index)
 {
-	u64 time_start;
-
-	time_start = local_clock_noinstr();
+	unsigned long flags;
 
 	dev->poll_time_limit = false;
 
 	raw_local_irq_enable();
 	if (!current_set_polling_and_test()) {
-		u64 limit;
-
-		limit = cpuidle_poll_time(drv, dev);
-
-		while (!need_resched()) {
-			unsigned int loop_count = 0;
-			if (local_clock_noinstr() - time_start > limit) {
-				dev->poll_time_limit = true;
-				break;
-			}
-
-			smp_cond_load_relaxed(&current_thread_info()->flags,
-					      VAL & _TIF_NEED_RESCHED ||
-					      loop_count++ >= POLL_IDLE_RELAX_COUNT);
-		}
+		u64 limit = cpuidle_poll_time(drv, dev);
+		flags = smp_vcond_load_relaxed(limit, &current_thread_info()->flags, _TIF_NEED_RESCHED, _TIF_NEED_RESCHED);
+		dev->poll_time_limit = !(flags & _TIF_NEED_RESCHED);
 	}
 	raw_local_irq_disable();