The thermal pressure mechanism consists of two parts: 1) PELT-like signal with its own clock (rq_clock_thermal()) which is responsible for the raising/decaying characteristics 2) instantaneous information provided in 'thermal_pressure' variable, which is set by thermal framework or drivers to notify about the throttling. Add a new mechanism which allows to change the raising/decaying characteristics of the PELT-like thermal signal. To make this happen modify how the rq_clock_thermal() counts. Instead of only slowing down the clock, which results in longer raising/decaying periods, make it faster. Thanks to that the information about throttling can faster arrive at the right place in the scheduler. This faster propagation of information is useful for the latency sensitive stuff, such as RT tasks. In a situation of CPU capacity inversion, such task might suffer when staying on the lower capacity CPU. Change the boot parameter 'sched_thermal_decay_shift' allowed values and use the negatives to speed up the thermal clock. Signed-off-by: Lukasz Luba <lukasz.luba@xxxxxxx> --- Hi all, This patch addresses an issue of missing configuration for the thermal pressure raising/decaying characteristic to be more instantaneous. This more sharp signal might be better if the raw thermal signal already has 'some logic' or doesn't change that often, like in IPA (every 100ms). I've prepared a notebook with experiments with different shifter values [0, -2, -3, -4, 2, 4] for IPA thermal update periods: 50ms, 100ms (and also jumping between cooling states 0, 1 or 0, 3). It presents two signals: instantaneous thermal update and thermal_load_avg(). It would be useful for discussion. I can provide more details if needed. Regards, Lukasz Luba [1] https://nbviewer.org/github/lukaszluba-arm/lisa/blob/public_tests/thermal_pressure_delays-all-ipa.ipynb Documentation/admin-guide/kernel-parameters.txt | 15 +++++++++++---- kernel/sched/fair.c | 2 +- kernel/sched/sched.h | 17 +++++++++++++++-- 3 files changed, 27 insertions(+), 7 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index c2d1f8b5e8f3..ba32540f1fbf 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5117,15 +5117,22 @@ pressure signal. Thermal pressure signal follows the default decay period of other scheduler pelt signals(usually 32 ms but configurable). Setting - sched_thermal_decay_shift will left shift the decay - period for the thermal pressure signal by the shift - value. + a positive value for sched_thermal_decay_shift will + left shift the decay period for the thermal pressure + signal by the shift value. This would make + raising/decaying characteristic longer. Setting + a negative value will right shift the decay period + by the shift value and make the raising/decaying + characteristic more sharp. i.e. with the default pelt decay period of 32 ms sched_thermal_decay_shift thermal pressure decay pr + -2 8 ms + -1 16 ms + 0 32 ms 1 64 ms 2 128 ms and so on. - Format: integer between 0 and 10 + Format: integer between -5 and 10 Default is 0. scftorture.holdoff= [KNL] diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 5146163bfabb..93cb7db5939c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -100,7 +100,7 @@ static int __init setup_sched_thermal_decay_shift(char *str) if (kstrtoint(str, 0, &_shift)) pr_warn("Unable to set scheduler thermal pressure decay shift parameter\n"); - sched_thermal_decay_shift = clamp(_shift, 0, 10); + sched_thermal_decay_shift = clamp(_shift, -5, 10); return 1; } __setup("sched_thermal_decay_shift=", setup_sched_thermal_decay_shift); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index de53be905739..cb453c0f3572 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1478,8 +1478,14 @@ static inline u64 rq_clock_task(struct rq *rq) /** * By default the decay is the default pelt decay period. * The decay shift can change the decay period in - * multiples of 32. + * multiples of 32 to make it longer or to make it shorter using + * negative values as on the example below. * Decay shift Decay period(ms) + * -5 1 + * -4 2 + * -3 4 + * -2 8 + * -1 16 * 0 32 * 1 64 * 2 128 @@ -1490,7 +1496,14 @@ extern int sched_thermal_decay_shift; static inline u64 rq_clock_thermal(struct rq *rq) { - return rq_clock_task(rq) >> sched_thermal_decay_shift; + u64 thermal_clock = rq_clock_task(rq); + + if (sched_thermal_decay_shift < 0) + thermal_clock <<= -sched_thermal_decay_shift; + else + thermal_clock >>= sched_thermal_decay_shift; + + return thermal_clock; } static inline void rq_clock_skip_update(struct rq *rq) -- 2.17.1
