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| author | Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com> | 2016-07-01 14:24:14 (GMT) |
|---|---|---|
| committer | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2016-07-04 12:17:34 (GMT) |
| commit | dbd1b8ea43b17e2ed4acda72f83ea17f69408682 (patch) | |
| tree | ee37f87df9d788548910546c9be84d5581803514 | |
| parent | 4c2e07c6a29e0129e975727b9f57eede813eea85 (diff) | |
| download | linux-dbd1b8ea43b17e2ed4acda72f83ea17f69408682.tar.xz | |
cpuidle: Fix last_residency division
Snooze is a poll idle state in powernv and pseries platforms. Snooze
has a timeout so that if a CPU stays in snooze for more than target
residency of the next available idle state, then it would exit
thereby giving chance to the cpuidle governor to re-evaluate and
promote the CPU to a deeper idle state. Therefore whenever snooze
exits due to this timeout, its last_residency will be target_residency
of the next deeper state.
Commit e93e59ce5b85 "cpuidle: Replace ktime_get() with local_clock()"
changed the math around last_residency calculation. Specifically,
while converting last_residency value from nano- to microseconds, it
carries out right shift by 10. Because of that, in snooze timeout
exit scenarios last_residency calculated is roughly 2.3% less than
target_residency of the next available state. This pattern is picked
up by get_typical_interval() in the menu governor and therefore
expected_interval in menu_select() is frequently less than the
target_residency of any state other than snooze.
Due to this we are entering snooze at a higher rate, thereby
affecting the single thread performance.
Fix this by using more precise division via ktime_us_delta().
Fixes: e93e59ce5b85 "cpuidle: Replace ktime_get() with local_clock()"
Reported-by: Anton Blanchard <anton@samba.org>
Bisected-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
Signed-off-by: Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
| -rw-r--r-- | drivers/cpuidle/cpuidle.c | 12 |
1 files changed, 4 insertions, 8 deletions
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c index a4d0059..c73207a 100644 --- a/drivers/cpuidle/cpuidle.c +++ b/drivers/cpuidle/cpuidle.c @@ -173,7 +173,7 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv, struct cpuidle_state *target_state = &drv->states[index]; bool broadcast = !!(target_state->flags & CPUIDLE_FLAG_TIMER_STOP); - u64 time_start, time_end; + ktime_t time_start, time_end; s64 diff; /* @@ -195,13 +195,13 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv, sched_idle_set_state(target_state); trace_cpu_idle_rcuidle(index, dev->cpu); - time_start = local_clock(); + time_start = ns_to_ktime(local_clock()); stop_critical_timings(); entered_state = target_state->enter(dev, drv, index); start_critical_timings(); - time_end = local_clock(); + time_end = ns_to_ktime(local_clock()); trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu); /* The cpu is no longer idle or about to enter idle. */ @@ -217,11 +217,7 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv, if (!cpuidle_state_is_coupled(drv, index)) local_irq_enable(); - /* - * local_clock() returns the time in nanosecond, let's shift - * by 10 (divide by 1024) to have microsecond based time. - */ - diff = (time_end - time_start) >> 10; + diff = ktime_us_delta(time_end, time_start); if (diff > INT_MAX) diff = INT_MAX; |