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authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2013-07-27 01:41:34 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-08-11 18:35:24 -0700
commitd201a0b94daa5d8f7126c81678ccc04f9215772a (patch)
tree8351e1bcfbff042d4de75fc53f6b61e6e47e739c
parente9ef4410a75bea04e5f9e30c41fba0ebfa9b7559 (diff)
downloadlinaro-lsk-d201a0b94daa5d8f7126c81678ccc04f9215772a.tar.gz
Revert "cpuidle: Quickly notice prediction failure for repeat mode"
commit 148519120c6d1f19ad53349683aeae9f228b0b8d upstream. Revert commit 69a37bea (cpuidle: Quickly notice prediction failure for repeat mode), because it has been identified as the source of a significant performance regression in v3.8 and later as explained by Jeremy Eder: We believe we've identified a particular commit to the cpuidle code that seems to be impacting performance of variety of workloads. The simplest way to reproduce is using netperf TCP_RR test, so we're using that, on a pair of Sandy Bridge based servers. We also have data from a large database setup where performance is also measurably/positively impacted, though that test data isn't easily share-able. Included below are test results from 3 test kernels: kernel reverts ----------------------------------------------------------- 1) vanilla upstream (no reverts) 2) perfteam2 reverts e11538d1f03914eb92af5a1a378375c05ae8520c 3) test reverts 69a37beabf1f0a6705c08e879bdd5d82ff6486c4 e11538d1f03914eb92af5a1a378375c05ae8520c In summary, netperf TCP_RR numbers improve by approximately 4% after reverting 69a37beabf1f0a6705c08e879bdd5d82ff6486c4. When 69a37beabf1f0a6705c08e879bdd5d82ff6486c4 is included, C0 residency never seems to get above 40%. Taking that patch out gets C0 near 100% quite often, and performance increases. The below data are histograms representing the %c0 residency @ 1-second sample rates (using turbostat), while under netperf test. - If you look at the first 4 histograms, you can see %c0 residency almost entirely in the 30,40% bin. - The last pair, which reverts 69a37beabf1f0a6705c08e879bdd5d82ff6486c4, shows %c0 in the 80,90,100% bins. Below each kernel name are netperf TCP_RR trans/s numbers for the particular kernel that can be disclosed publicly, comparing the 3 test kernels. We ran a 4th test with the vanilla kernel where we've also set /dev/cpu_dma_latency=0 to show overall impact boosting single-threaded TCP_RR performance over 11% above baseline. 3.10-rc2 vanilla RX + c0 lock (/dev/cpu_dma_latency=0): TCP_RR trans/s 54323.78 ----------------------------------------------------------- 3.10-rc2 vanilla RX (no reverts) TCP_RR trans/s 48192.47 Receiver %c0 0.0000 - 10.0000 [ 1]: * 10.0000 - 20.0000 [ 0]: 20.0000 - 30.0000 [ 0]: 30.0000 - 40.0000 [ 59]: *********************************************************** 40.0000 - 50.0000 [ 1]: * 50.0000 - 60.0000 [ 0]: 60.0000 - 70.0000 [ 0]: 70.0000 - 80.0000 [ 0]: 80.0000 - 90.0000 [ 0]: 90.0000 - 100.0000 [ 0]: Sender %c0 0.0000 - 10.0000 [ 1]: * 10.0000 - 20.0000 [ 0]: 20.0000 - 30.0000 [ 0]: 30.0000 - 40.0000 [ 11]: *********** 40.0000 - 50.0000 [ 49]: ************************************************* 50.0000 - 60.0000 [ 0]: 60.0000 - 70.0000 [ 0]: 70.0000 - 80.0000 [ 0]: 80.0000 - 90.0000 [ 0]: 90.0000 - 100.0000 [ 0]: ----------------------------------------------------------- 3.10-rc2 perfteam2 RX (reverts commit e11538d1f03914eb92af5a1a378375c05ae8520c) TCP_RR trans/s 49698.69 Receiver %c0 0.0000 - 10.0000 [ 1]: * 10.0000 - 20.0000 [ 1]: * 20.0000 - 30.0000 [ 0]: 30.0000 - 40.0000 [ 59]: *********************************************************** 40.0000 - 50.0000 [ 0]: 50.0000 - 60.0000 [ 0]: 60.0000 - 70.0000 [ 0]: 70.0000 - 80.0000 [ 0]: 80.0000 - 90.0000 [ 0]: 90.0000 - 100.0000 [ 0]: Sender %c0 0.0000 - 10.0000 [ 1]: * 10.0000 - 20.0000 [ 0]: 20.0000 - 30.0000 [ 0]: 30.0000 - 40.0000 [ 2]: ** 40.0000 - 50.0000 [ 58]: ********************************************************** 50.0000 - 60.0000 [ 0]: 60.0000 - 70.0000 [ 0]: 70.0000 - 80.0000 [ 0]: 80.0000 - 90.0000 [ 0]: 90.0000 - 100.0000 [ 0]: ----------------------------------------------------------- 3.10-rc2 test RX (reverts 69a37beabf1f0a6705c08e879bdd5d82ff6486c4 and e11538d1f03914eb92af5a1a378375c05ae8520c) TCP_RR trans/s 47766.95 Receiver %c0 0.0000 - 10.0000 [ 1]: * 10.0000 - 20.0000 [ 1]: * 20.0000 - 30.0000 [ 0]: 30.0000 - 40.0000 [ 27]: *************************** 40.0000 - 50.0000 [ 2]: ** 50.0000 - 60.0000 [ 0]: 60.0000 - 70.0000 [ 2]: ** 70.0000 - 80.0000 [ 0]: 80.0000 - 90.0000 [ 0]: 90.0000 - 100.0000 [ 28]: **************************** Sender: 0.0000 - 10.0000 [ 1]: * 10.0000 - 20.0000 [ 0]: 20.0000 - 30.0000 [ 0]: 30.0000 - 40.0000 [ 11]: *********** 40.0000 - 50.0000 [ 0]: 50.0000 - 60.0000 [ 1]: * 60.0000 - 70.0000 [ 0]: 70.0000 - 80.0000 [ 3]: *** 80.0000 - 90.0000 [ 7]: ******* 90.0000 - 100.0000 [ 38]: ************************************** These results demonstrate gaining back the tendency of the CPU to stay in more responsive, performant C-states (and thus yield measurably better performance), by reverting commit 69a37beabf1f0a6705c08e879bdd5d82ff6486c4. Requested-by: Jeremy Eder <jeder@redhat.com> Tested-by: Len Brown <len.brown@intel.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/cpuidle/governors/menu.c73
-rw-r--r--include/linux/tick.h6
-rw-r--r--kernel/time/tick-sched.c9
3 files changed, 6 insertions, 82 deletions
diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index b69a87e2215..bc580b67a65 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -28,13 +28,6 @@
#define MAX_INTERESTING 50000
#define STDDEV_THRESH 400
-/* 60 * 60 > STDDEV_THRESH * INTERVALS = 400 * 8 */
-#define MAX_DEVIATION 60
-
-static DEFINE_PER_CPU(struct hrtimer, menu_hrtimer);
-static DEFINE_PER_CPU(int, hrtimer_status);
-/* menu hrtimer mode */
-enum {MENU_HRTIMER_STOP, MENU_HRTIMER_REPEAT};
/*
* Concepts and ideas behind the menu governor
@@ -198,42 +191,17 @@ static u64 div_round64(u64 dividend, u32 divisor)
return div_u64(dividend + (divisor / 2), divisor);
}
-/* Cancel the hrtimer if it is not triggered yet */
-void menu_hrtimer_cancel(void)
-{
- int cpu = smp_processor_id();
- struct hrtimer *hrtmr = &per_cpu(menu_hrtimer, cpu);
-
- /* The timer is still not time out*/
- if (per_cpu(hrtimer_status, cpu)) {
- hrtimer_cancel(hrtmr);
- per_cpu(hrtimer_status, cpu) = MENU_HRTIMER_STOP;
- }
-}
-EXPORT_SYMBOL_GPL(menu_hrtimer_cancel);
-
-/* Call back for hrtimer is triggered */
-static enum hrtimer_restart menu_hrtimer_notify(struct hrtimer *hrtimer)
-{
- int cpu = smp_processor_id();
-
- per_cpu(hrtimer_status, cpu) = MENU_HRTIMER_STOP;
-
- return HRTIMER_NORESTART;
-}
-
/*
* Try detecting repeating patterns by keeping track of the last 8
* intervals, and checking if the standard deviation of that set
* of points is below a threshold. If it is... then use the
* average of these 8 points as the estimated value.
*/
-static u32 get_typical_interval(struct menu_device *data)
+static void get_typical_interval(struct menu_device *data)
{
int i = 0, divisor = 0;
uint64_t max = 0, avg = 0, stddev = 0;
int64_t thresh = LLONG_MAX; /* Discard outliers above this value. */
- unsigned int ret = 0;
again:
@@ -274,16 +242,13 @@ again:
if (((avg > stddev * 6) && (divisor * 4 >= INTERVALS * 3))
|| stddev <= 20) {
data->predicted_us = avg;
- ret = 1;
- return ret;
+ return;
} else if ((divisor * 4) > INTERVALS * 3) {
/* Exclude the max interval */
thresh = max - 1;
goto again;
}
-
- return ret;
}
/**
@@ -298,9 +263,6 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
int i;
int multiplier;
struct timespec t;
- int repeat = 0, low_predicted = 0;
- int cpu = smp_processor_id();
- struct hrtimer *hrtmr = &per_cpu(menu_hrtimer, cpu);
if (data->needs_update) {
menu_update(drv, dev);
@@ -335,7 +297,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
data->predicted_us = div_round64(data->expected_us * data->correction_factor[data->bucket],
RESOLUTION * DECAY);
- repeat = get_typical_interval(data);
+ get_typical_interval(data);
/*
* We want to default to C1 (hlt), not to busy polling
@@ -356,10 +318,8 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
if (s->disabled || su->disable)
continue;
- if (s->target_residency > data->predicted_us) {
- low_predicted = 1;
+ if (s->target_residency > data->predicted_us)
continue;
- }
if (s->exit_latency > latency_req)
continue;
if (s->exit_latency * multiplier > data->predicted_us)
@@ -369,28 +329,6 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
data->exit_us = s->exit_latency;
}
- /* not deepest C-state chosen for low predicted residency */
- if (low_predicted) {
- unsigned int timer_us = 0;
-
- /*
- * Set a timer to detect whether this sleep is much
- * longer than repeat mode predicted. If the timer
- * triggers, the code will evaluate whether to put
- * the CPU into a deeper C-state.
- * The timer is cancelled on CPU wakeup.
- */
- timer_us = 2 * (data->predicted_us + MAX_DEVIATION);
-
- if (repeat && (4 * timer_us < data->expected_us)) {
- RCU_NONIDLE(hrtimer_start(hrtmr,
- ns_to_ktime(1000 * timer_us),
- HRTIMER_MODE_REL_PINNED));
- /* In repeat case, menu hrtimer is started */
- per_cpu(hrtimer_status, cpu) = MENU_HRTIMER_REPEAT;
- }
- }
-
return data->last_state_idx;
}
@@ -481,9 +419,6 @@ static int menu_enable_device(struct cpuidle_driver *drv,
struct cpuidle_device *dev)
{
struct menu_device *data = &per_cpu(menu_devices, dev->cpu);
- struct hrtimer *t = &per_cpu(menu_hrtimer, dev->cpu);
- hrtimer_init(t, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
- t->function = menu_hrtimer_notify;
memset(data, 0, sizeof(struct menu_device));
diff --git a/include/linux/tick.h b/include/linux/tick.h
index 9180f4b85e6..62bd8b72873 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -174,10 +174,4 @@ static inline void tick_nohz_task_switch(struct task_struct *tsk) { }
#endif
-# ifdef CONFIG_CPU_IDLE_GOV_MENU
-extern void menu_hrtimer_cancel(void);
-# else
-static inline void menu_hrtimer_cancel(void) {}
-# endif /* CONFIG_CPU_IDLE_GOV_MENU */
-
#endif
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 0cf1c145318..4251374578b 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -832,13 +832,10 @@ void tick_nohz_irq_exit(void)
{
struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
- if (ts->inidle) {
- /* Cancel the timer because CPU already waken up from the C-states*/
- menu_hrtimer_cancel();
+ if (ts->inidle)
__tick_nohz_idle_enter(ts);
- } else {
+ else
tick_nohz_full_stop_tick(ts);
- }
}
/**
@@ -936,8 +933,6 @@ void tick_nohz_idle_exit(void)
ts->inidle = 0;
- /* Cancel the timer because CPU already waken up from the C-states*/
- menu_hrtimer_cancel();
if (ts->idle_active || ts->tick_stopped)
now = ktime_get();