Revert "cpuidle: Quickly notice prediction failure for repeat mode"
Revert commit69a37bea(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 revertse11538d1f03) test reverts69a37beabfe11538d1f0In summary, netperf TCP_RR numbers improve by approximately 4% after reverting69a37beabf. When69a37beabfis 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 reverts69a37beabf, 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 commite11538d1f0) 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 (reverts69a37beabfande11538d1f0) 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 commit69a37beabf. Requested-by: Jeremy Eder <jeder@redhat.com> Tested-by: Len Brown <len.brown@intel.com> Cc: 3.8+ <stable@vger.kernel.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Rafael J. Wysocki
Родитель
228b30234f
Коммит
148519120c
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@ -28,13 +28,6 @@
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#define MAX_INTERESTING 50000
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#define STDDEV_THRESH 400
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/* 60 * 60 > STDDEV_THRESH * INTERVALS = 400 * 8 */
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#define MAX_DEVIATION 60
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static DEFINE_PER_CPU(struct hrtimer, menu_hrtimer);
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static DEFINE_PER_CPU(int, hrtimer_status);
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/* menu hrtimer mode */
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enum {MENU_HRTIMER_STOP, MENU_HRTIMER_REPEAT};
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/*
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* Concepts and ideas behind the menu governor
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@ -198,42 +191,17 @@ static u64 div_round64(u64 dividend, u32 divisor)
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return div_u64(dividend + (divisor / 2), divisor);
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}
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/* Cancel the hrtimer if it is not triggered yet */
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void menu_hrtimer_cancel(void)
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{
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int cpu = smp_processor_id();
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struct hrtimer *hrtmr = &per_cpu(menu_hrtimer, cpu);
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/* The timer is still not time out*/
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if (per_cpu(hrtimer_status, cpu)) {
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hrtimer_cancel(hrtmr);
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per_cpu(hrtimer_status, cpu) = MENU_HRTIMER_STOP;
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}
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}
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EXPORT_SYMBOL_GPL(menu_hrtimer_cancel);
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/* Call back for hrtimer is triggered */
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static enum hrtimer_restart menu_hrtimer_notify(struct hrtimer *hrtimer)
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{
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int cpu = smp_processor_id();
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per_cpu(hrtimer_status, cpu) = MENU_HRTIMER_STOP;
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return HRTIMER_NORESTART;
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}
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/*
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* Try detecting repeating patterns by keeping track of the last 8
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* intervals, and checking if the standard deviation of that set
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* of points is below a threshold. If it is... then use the
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* average of these 8 points as the estimated value.
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*/
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static u32 get_typical_interval(struct menu_device *data)
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static void get_typical_interval(struct menu_device *data)
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{
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int i = 0, divisor = 0;
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uint64_t max = 0, avg = 0, stddev = 0;
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int64_t thresh = LLONG_MAX; /* Discard outliers above this value. */
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unsigned int ret = 0;
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again:
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@ -274,16 +242,13 @@ again:
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if (((avg > stddev * 6) && (divisor * 4 >= INTERVALS * 3))
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|| stddev <= 20) {
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data->predicted_us = avg;
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ret = 1;
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return ret;
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return;
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} else if ((divisor * 4) > INTERVALS * 3) {
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/* Exclude the max interval */
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thresh = max - 1;
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goto again;
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}
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return ret;
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}
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/**
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@ -298,9 +263,6 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
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int i;
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int multiplier;
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struct timespec t;
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int repeat = 0, low_predicted = 0;
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int cpu = smp_processor_id();
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struct hrtimer *hrtmr = &per_cpu(menu_hrtimer, cpu);
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if (data->needs_update) {
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menu_update(drv, dev);
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@ -335,7 +297,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
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data->predicted_us = div_round64(data->expected_us * data->correction_factor[data->bucket],
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RESOLUTION * DECAY);
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repeat = get_typical_interval(data);
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get_typical_interval(data);
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/*
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* We want to default to C1 (hlt), not to busy polling
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@ -356,10 +318,8 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
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if (s->disabled || su->disable)
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continue;
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if (s->target_residency > data->predicted_us) {
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low_predicted = 1;
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if (s->target_residency > data->predicted_us)
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continue;
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}
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if (s->exit_latency > latency_req)
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continue;
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if (s->exit_latency * multiplier > data->predicted_us)
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@ -369,28 +329,6 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
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data->exit_us = s->exit_latency;
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}
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/* not deepest C-state chosen for low predicted residency */
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if (low_predicted) {
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unsigned int timer_us = 0;
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/*
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* Set a timer to detect whether this sleep is much
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* longer than repeat mode predicted. If the timer
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* triggers, the code will evaluate whether to put
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* the CPU into a deeper C-state.
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* The timer is cancelled on CPU wakeup.
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*/
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timer_us = 2 * (data->predicted_us + MAX_DEVIATION);
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if (repeat && (4 * timer_us < data->expected_us)) {
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RCU_NONIDLE(hrtimer_start(hrtmr,
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ns_to_ktime(1000 * timer_us),
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HRTIMER_MODE_REL_PINNED));
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/* In repeat case, menu hrtimer is started */
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per_cpu(hrtimer_status, cpu) = MENU_HRTIMER_REPEAT;
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}
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}
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return data->last_state_idx;
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}
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@ -481,9 +419,6 @@ static int menu_enable_device(struct cpuidle_driver *drv,
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struct cpuidle_device *dev)
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{
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struct menu_device *data = &per_cpu(menu_devices, dev->cpu);
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struct hrtimer *t = &per_cpu(menu_hrtimer, dev->cpu);
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hrtimer_init(t, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
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t->function = menu_hrtimer_notify;
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memset(data, 0, sizeof(struct menu_device));
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@ -174,10 +174,4 @@ static inline void tick_nohz_task_switch(struct task_struct *tsk) { }
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#endif
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# ifdef CONFIG_CPU_IDLE_GOV_MENU
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extern void menu_hrtimer_cancel(void);
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# else
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static inline void menu_hrtimer_cancel(void) {}
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# endif /* CONFIG_CPU_IDLE_GOV_MENU */
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#endif
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@ -827,13 +827,10 @@ void tick_nohz_irq_exit(void)
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{
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struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
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if (ts->inidle) {
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/* Cancel the timer because CPU already waken up from the C-states*/
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menu_hrtimer_cancel();
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if (ts->inidle)
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__tick_nohz_idle_enter(ts);
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} else {
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else
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tick_nohz_full_stop_tick(ts);
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}
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}
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/**
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@ -931,8 +928,6 @@ void tick_nohz_idle_exit(void)
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ts->inidle = 0;
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/* Cancel the timer because CPU already waken up from the C-states*/
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menu_hrtimer_cancel();
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if (ts->idle_active || ts->tick_stopped)
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now = ktime_get();
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