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cpuidle: poll_state: Revise loop termination condition

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If need_resched() returns "false", breaking out of the loop in
poll_idle() will cause a new idle state to be selected, so in fact
it usually doesn't make sense to spin in it longer than the target
residency of the second state.  [Note that the "polling" state is
used only if there is at least one "real" state defined in addition
to it, so the second state is always there.]  On the other hand,
breaking out of it early (say in case the next state is disabled)
shouldn't hurt as it is polling anyway.

For this reason, make the loop in poll_idle() break if the CPU has
been spinning longer than the target residency of the second state
(the "polling" state can only be state[0]).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Rafael J. Wysocki 2018-10-02 23:50:30 +02:00
parent 53812cdc91
commit 01bad1c689
1 changed files with 2 additions and 2 deletions
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4
drivers/cpuidle/poll_state.c
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@ -9,7 +9,6 @@
#include <linux/sched/clock.h> #include <linux/sched/clock.h>
#include <linux/sched/idle.h> #include <linux/sched/idle.h>
#define POLL_IDLE_TIME_LIMIT (TICK_NSEC / 16)
#define POLL_IDLE_RELAX_COUNT 200 #define POLL_IDLE_RELAX_COUNT 200
static int __cpuidle poll_idle(struct cpuidle_device *dev, static int __cpuidle poll_idle(struct cpuidle_device *dev,
@ -21,6 +20,7 @@ static int __cpuidle poll_idle(struct cpuidle_device *dev,
local_irq_enable(); local_irq_enable();
if (!current_set_polling_and_test()) { if (!current_set_polling_and_test()) {
u64 limit = (u64)drv->states[1].target_residency * NSEC_PER_USEC;
unsigned int loop_count = 0; unsigned int loop_count = 0;
while (!need_resched()) { while (!need_resched()) {
@ -29,7 +29,7 @@ static int __cpuidle poll_idle(struct cpuidle_device *dev,
continue; continue;
loop_count = 0; loop_count = 0;
if (local_clock() - time_start > POLL_IDLE_TIME_LIMIT) { if (local_clock() - time_start > limit) {
dev->poll_time_limit = true; dev->poll_time_limit = true;
break; break;
} }