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linux-next/drivers/cpuidle/poll_state.c
Rafael J. Wysocki 4dc2375c1a 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>
2018-03-29 13:06:08 +02:00

53 lines
1.2 KiB
C

/*
* poll_state.c - Polling idle state
*
* This file is released under the GPLv2.
*/
#include <linux/cpuidle.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>
#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)
{
u64 time_start = local_clock();
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;
}
}
current_clr_polling();
return index;
}
void cpuidle_poll_state_init(struct cpuidle_driver *drv)
{
struct cpuidle_state *state = &drv->states[0];
snprintf(state->name, CPUIDLE_NAME_LEN, "POLL");
snprintf(state->desc, CPUIDLE_DESC_LEN, "CPUIDLE CORE POLL IDLE");
state->exit_latency = 0;
state->target_residency = 0;
state->power_usage = -1;
state->enter = poll_idle;
state->disabled = false;
state->flags = CPUIDLE_FLAG_POLLING;
}
EXPORT_SYMBOL_GPL(cpuidle_poll_state_init);