From 4dc2375c1a4e88ed2701f6961e0e4f9a7696ad3c Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Tue, 27 Mar 2018 23:58:45 +0200 Subject: 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 Reported-by: Doug Smythies Signed-off-by: Rafael J. Wysocki Tested-by: Rik van Riel Reviewed-by: Rik van Riel --- drivers/cpuidle/poll_state.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'drivers/cpuidle') diff --git a/drivers/cpuidle/poll_state.c b/drivers/cpuidle/poll_state.c index 68cdc50..3f86d23 100644 --- a/drivers/cpuidle/poll_state.c +++ b/drivers/cpuidle/poll_state.c @@ -10,6 +10,7 @@ #include #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; } -- cgit v1.1