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cpuidle: poll_state: Avoid invoking local_clock() too often

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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>
This commit is contained in:
Rafael J. Wysocki 2018-03-27 23:58:45 +02:00
parent 64bdff6980
commit 4dc2375c1a
1 changed files with 6 additions and 0 deletions
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6
drivers/cpuidle/poll_state.c
View file

@ -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;
}