| Message ID | 1534090171-14464-1-git-send-email-leo.yan@linaro.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | Improvement stopping tick decision making in 'menu' idle governor | expand |
On Sunday, August 12, 2018 6:09:26 PM CEST Leo Yan wrote: > We found the CPU cannot stay in deepest idle state as expected with > running synthetic workloads with mainline kernel on Arm platform > (96boards Hikey620 with octa CA53 CPUs). > > The main issue is the criteria for decision stopping tick; now > the criteria is checking expected interval is less than TICK_USEC, but > this doesn't consider the next tick detla is float due CPU randomly > eneters and exits idle states; furthermore, it's stick to checking > TICK_USEC as boundary for decision stopping tick, unfortunately this has > hole to select a shallow state with stopping tick, so the CPU stays in > shallow state for long time. > > This patch series is to explore more reasonable making decision for > stopping tick and the most important fixing is to avoid powernightmares > issue after we apply these criterias for making decisions. Patches > 0001 ~ 0003 are used to refactor the variables and structures for more > readable code, it also provides a function menu_decide_stopping_tick() > which can be used to encapsulate the making decision logics. The last > two patches are primary for improvement, patch 0004 'cpuidle: menu: > Don't stay in shallow state for a long time' introduces a new criteria > (it's a more strict criteria than before) for not stopping tick for > shallow state cases; patch 0005 is use the dynamic tick detla to replace > the static value TICK_USEC for decision if the tick is expired before or > after the prediction, according this comparison we can get conclusion if > need to stop tick or not. > > With more accurate decision for stopping tick, one immediate benefit is > the CPUs have more chance to stay in deepest state, it also can avoid to > run tick unnecessarily and so avoid a shallower state introduced by tick > event. For the testing result in below table, we can see the result > proves the improvement by better stopping tick decision making in this > patch series, we run the workload generated by rt-app (a single task > with period 5ms and duty cycle 1%/3%/5%/10%/20%/30%/40%), the total > running time is 60s. We do statistics for all CPUs for all idle states > duration, the unit is second (s), for cases (dutycycle=1%/3%/5%/10%/20%) > we can see the shallow state C0/C1 duration are reduced and the time > has been moved to deepest state, so the deepest state C2 duration can > have improvement for ~9s to ~21s. for cases (dutycycle=30%/40%) though > we can see the deepest state durations are parity between with and > without patch series, but it has a minor improvement for C1 state > duration by stealing C0 state duration. > > Some notations are used in the table: > > state: C0: WFI; C1: CPU OFF; C2: Cluster OFF > > All testing cases have single task with 5ms period: > > Without patches With patches Difference > ----------------------- ----------------------- -------------------------- > Duty cycle C0 C1 C2 C0 C1 C2 C0 C1 C2 > 1% 2.397 16.528 471.905 0.916 2.688 487.328 -1.481 -13.840 +15.422 > 3% 3.957 20.541 464.434 1.510 2.398 485.914 -2.447 -18.143 +21.480 > 5% 2.866 8.609 474.777 1.166 2.250 483.983 -1.699 -6.359 +9.205 > 10% 2.893 28.753 453.277 1.147 14.134 469.190 -1.745 -14.618 +15.913 > 20% 7.620 41.086 431.735 1.595 35.055 442.482 -6.024 -6.030 +10.747 > 30% 4.394 38.328 431.442 1.964 40.857 430.973 -2.430 +2.529 -0.468 > 40% 7.390 29.415 430.914 1.789 34.832 431.588 -5.600 +5.417 -0.673 > > > P.s. for the testing, applied Rafael's patch 'cpuidle: menu: Handle > stopped tick more aggressively' [1] to avoid select unexpected shallow > state after tick has been stopped. > > [1] https://lkml.org/lkml/2018/8/10/259 > > Leo Yan (5): > cpuidle: menu: Clean up variables usage in menu_select() > cpuidle: menu: Record tick delta value in struct menu_device > cpuidle: menu: Provide menu_decide_stopping_tick() > cpuidle: menu: Don't stay in shallow state for a long time > cpuidle: menu: Change to compare prediction with tick delta > > drivers/cpuidle/governors/menu.c | 104 ++++++++++++++++++++++++++++----------- > 1 file changed, 76 insertions(+), 28 deletions(-) > > Overall, I don't like this series, sorry about that. The majority of changes in it are code reorganization, quite questionable in a couple of cases, and a similar goal can be achieved with a very simple patch that I'm going to post shortly. Thanks, Rafael
We found the CPU cannot stay in deepest idle state as expected with running synthetic workloads with mainline kernel on Arm platform (96boards Hikey620 with octa CA53 CPUs). The main issue is the criteria for decision stopping tick; now the criteria is checking expected interval is less than TICK_USEC, but this doesn't consider the next tick detla is float due CPU randomly eneters and exits idle states; furthermore, it's stick to checking TICK_USEC as boundary for decision stopping tick, unfortunately this has hole to select a shallow state with stopping tick, so the CPU stays in shallow state for long time. This patch series is to explore more reasonable making decision for stopping tick and the most important fixing is to avoid powernightmares issue after we apply these criterias for making decisions. Patches 0001 ~ 0003 are used to refactor the variables and structures for more readable code, it also provides a function menu_decide_stopping_tick() which can be used to encapsulate the making decision logics. The last two patches are primary for improvement, patch 0004 'cpuidle: menu: Don't stay in shallow state for a long time' introduces a new criteria (it's a more strict criteria than before) for not stopping tick for shallow state cases; patch 0005 is use the dynamic tick detla to replace the static value TICK_USEC for decision if the tick is expired before or after the prediction, according this comparison we can get conclusion if need to stop tick or not. With more accurate decision for stopping tick, one immediate benefit is the CPUs have more chance to stay in deepest state, it also can avoid to run tick unnecessarily and so avoid a shallower state introduced by tick event. For the testing result in below table, we can see the result proves the improvement by better stopping tick decision making in this patch series, we run the workload generated by rt-app (a single task with period 5ms and duty cycle 1%/3%/5%/10%/20%/30%/40%), the total running time is 60s. We do statistics for all CPUs for all idle states duration, the unit is second (s), for cases (dutycycle=1%/3%/5%/10%/20%) we can see the shallow state C0/C1 duration are reduced and the time has been moved to deepest state, so the deepest state C2 duration can have improvement for ~9s to ~21s. for cases (dutycycle=30%/40%) though we can see the deepest state durations are parity between with and without patch series, but it has a minor improvement for C1 state duration by stealing C0 state duration. Some notations are used in the table: state: C0: WFI; C1: CPU OFF; C2: Cluster OFF All testing cases have single task with 5ms period: Without patches With patches Difference ----------------------- ----------------------- -------------------------- Duty cycle C0 C1 C2 C0 C1 C2 C0 C1 C2 1% 2.397 16.528 471.905 0.916 2.688 487.328 -1.481 -13.840 +15.422 3% 3.957 20.541 464.434 1.510 2.398 485.914 -2.447 -18.143 +21.480 5% 2.866 8.609 474.777 1.166 2.250 483.983 -1.699 -6.359 +9.205 10% 2.893 28.753 453.277 1.147 14.134 469.190 -1.745 -14.618 +15.913 20% 7.620 41.086 431.735 1.595 35.055 442.482 -6.024 -6.030 +10.747 30% 4.394 38.328 431.442 1.964 40.857 430.973 -2.430 +2.529 -0.468 40% 7.390 29.415 430.914 1.789 34.832 431.588 -5.600 +5.417 -0.673 P.s. for the testing, applied Rafael's patch 'cpuidle: menu: Handle stopped tick more aggressively' [1] to avoid select unexpected shallow state after tick has been stopped. [1] https://lkml.org/lkml/2018/8/10/259 Leo Yan (5): cpuidle: menu: Clean up variables usage in menu_select() cpuidle: menu: Record tick delta value in struct menu_device cpuidle: menu: Provide menu_decide_stopping_tick() cpuidle: menu: Don't stay in shallow state for a long time cpuidle: menu: Change to compare prediction with tick delta drivers/cpuidle/governors/menu.c | 104 ++++++++++++++++++++++++++++----------- 1 file changed, 76 insertions(+), 28 deletions(-)