From: Christoph Lameter <cl@gentwo.org>
Date: Wed, 9 Oct 2024 02:46:56 +0000 (-0700)
Subject: Implement waiting using WFET
X-Git-Url: https://gentwo.org/gitweb/?a=commitdiff_plain;h=refs%2Fheads%2Fb4%2Fhaltpoll;p=linux%2F.git

Implement waiting using WFET
---

diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
index 61df2395585e..24acd9d093f1 100644
--- a/drivers/cpuidle/poll_state.c
+++ b/drivers/cpuidle/poll_state.c
@@ -8,44 +8,41 @@
 #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
-
 static int __cpuidle poll_idle(struct cpuidle_device *dev,
 			       struct cpuidle_driver *drv, int index)
 {
 	u64 time_start;
 
-	time_start = local_clock_noinstr();
+	time_start = get_cycles();
 
 	dev->poll_time_limit = false;
 
 	raw_local_irq_enable();
 	if (!current_set_polling_and_test()) {
-		u64 limit;
+		u64 end;
 
-		limit = cpuidle_poll_time(drv, dev);
+		end = start + NSECS_TO_CYCLES(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;
+
+			if (alternative_has_cap_unlikely(ARM64_HAS_WFXT)) {
+
+				/* We can power down for a configurable interval while waiting for event */
+				while (!need_resched() && get_cycles() < end)
+						wfet(end);
+
+			} else if (arch_timer_evtstrm_available()) {
+
+				/* We can power down for a ARCH_TIMER_EVT_STREAM_PERIOD_US time interval while waiting */
+				while (!need_resched() && (get_cycles() < end)
+						wfe();
+			} else {
+
+				/* No hardware wait mechanism. Do a polling loop */
+				while (!need_resched() && get_cycles() < end)
+					cpu_relax;
 			}
 
-			smp_cond_load_relaxed(&current_thread_info()->flags,
-					      VAL & _TIF_NEED_RESCHED ||
-					      loop_count++ >= POLL_IDLE_RELAX_COUNT);
 		}
 	}
 	raw_local_irq_disable();