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authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2018-03-27 23:58:45 +0200
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2018-03-29 13:06:08 +0200
commit4dc2375c1a4e88ed2701f6961e0e4f9a7696ad3c (patch)
tree926f002833a8fc9afe9aaae3bc71114c43f9b0b7 /drivers/cpuidle/poll_state.c
parent64bdff698092aa6be28c3b248f887022eec77902 (diff)
downloadlinux-4dc2375c1a4e88ed2701f6961e0e4f9a7696ad3c.tar.bz2
cpuidle: poll_state: Avoid invoking local_clock() too often
Rik reports that he sees an increase in CPU use in one benchmark due to commit 612f1a22f067 "cpuidle: poll_state: Add time limit to poll_idle()" that caused poll_idle() to call local_clock() in every iteration of the loop. Utilization increase generally means more non-idle time with respect to total CPU time (on the average) which implies reduced CPU frequency. Doug reports that limiting the rate of local_clock() invocations in there causes much less power to be drawn during a CPU-intensive parallel workload (with idle states 1 and 2 disabled to enforce more state 0 residency). These two reports together suggest that executing local_clock() on multiple CPUs in parallel at a high rate may cause chips to get hot and trigger thermal/power limits on them to kick in, so reduce the rate of local_clock() invocations in poll_idle() to avoid that issue. Fixes: 612f1a22f067 "cpuidle: poll_state: Add time limit to poll_idle()" Reported-by: Rik van Riel <riel@surriel.com> Reported-by: Doug Smythies <dsmythies@telus.net> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Tested-by: Rik van Riel <riel@surriel.com> Reviewed-by: Rik van Riel <riel@surriel.com>
Diffstat (limited to 'drivers/cpuidle/poll_state.c')
-rw-r--r--drivers/cpuidle/poll_state.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c
index 68cdc506524b..3f86d23c592e 100644
--- a/drivers/cpuidle/poll_state.c
+++ b/drivers/cpuidle/poll_state.c
@@ -10,6 +10,7 @@
#include <linux/sched/idle.h>
#define POLL_IDLE_TIME_LIMIT (TICK_NSEC / 16)
+#define POLL_IDLE_RELAX_COUNT 200
static int __cpuidle poll_idle(struct cpuidle_device *dev,
struct cpuidle_driver *drv, int index)
@@ -18,9 +19,14 @@ static int __cpuidle poll_idle(struct cpuidle_device *dev,
local_irq_enable();
if (!current_set_polling_and_test()) {
+ unsigned int loop_count = 0;
+
while (!need_resched()) {
cpu_relax();
+ if (loop_count++ < POLL_IDLE_RELAX_COUNT)
+ continue;
+ loop_count = 0;
if (local_clock() - time_start > POLL_IDLE_TIME_LIMIT)
break;
}