Messages in this thread | | | Date | Mon, 28 Oct 2019 16:21:35 +0100 | From | Peter Zijlstra <> | Subject | Re: [Patch v4 2/6] sched: Add infrastructure to store and update instantaneous thermal pressure |
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On Tue, Oct 22, 2019 at 04:34:21PM -0400, Thara Gopinath wrote: > Add thermal.c and thermal.h files that provides interface > APIs to initialize, update/average, track, accumulate and decay > thermal pressure per cpu basis. A per cpu variable delta_capacity is > introduced to keep track of instantaneous per cpu thermal pressure. > Thermal pressure is the delta between maximum capacity and capped > capacity due to a thermal event.
> API trigger_thermal_pressure_average is called for periodic accumulate > and decay of the thermal pressure. It is to to be called from a > periodic tick function. This API passes on the instantaneous delta > capacity of a cpu to update_thermal_load_avg to do the necessary > accumulate, decay and average.
> API update_thermal_pressure is for the system to update the thermal > pressure by providing a capped frequency ratio.
> Considering, trigger_thermal_pressure_average reads delta_capacity and > update_thermal_pressure writes into delta_capacity, one can argue for > some sort of locking mechanism to avoid a stale value.
> But considering trigger_thermal_pressure_average can be called from a > system critical path like scheduler tick function, a locking mechanism > is not ideal. This means that it is possible the delta_capacity value > used to calculate average thermal pressure for a cpu can be > stale for upto 1 tick period.
Please use a blank line at the end of a paragraph.
> Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org> > ---
> include/linux/sched.h | 8 ++++++++ > kernel/sched/Makefile | 2 +- > kernel/sched/thermal.c | 45 +++++++++++++++++++++++++++++++++++++++++++++ > kernel/sched/thermal.h | 13 +++++++++++++ > 4 files changed, 67 insertions(+), 1 deletion(-) > create mode 100644 kernel/sched/thermal.c > create mode 100644 kernel/sched/thermal.h
These are some tiny files, do these functions really need their own little files?
> diff --git a/kernel/sched/thermal.c b/kernel/sched/thermal.c > new file mode 100644 > index 0000000..0c84960 > --- /dev/null > +++ b/kernel/sched/thermal.c > @@ -0,0 +1,45 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * Scheduler Thermal Interactions > + * > + * Copyright (C) 2018 Linaro, Inc., Thara Gopinath <thara.gopinath@linaro.org> > + */ > + > +#include <linux/sched.h> > +#include "sched.h" > +#include "pelt.h" > +#include "thermal.h" > + > +static DEFINE_PER_CPU(unsigned long, delta_capacity); > + > +/** > + * update_thermal_pressure: Update thermal pressure > + * @cpu: the cpu for which thermal pressure is to be updated for > + * @capped_freq_ratio: capped max frequency << SCHED_CAPACITY_SHIFT / max freq > + * > + * capped_freq_ratio is normalized into capped capacity and the delta between > + * the arch_scale_cpu_capacity and capped capacity is stored in per cpu > + * delta_capacity. > + */ > +void update_thermal_pressure(int cpu, u64 capped_freq_ratio) > +{ > + unsigned long __capacity, delta; > + > + /* Normalize the capped freq ratio */ > + __capacity = (capped_freq_ratio * arch_scale_cpu_capacity(cpu)) >> > + SCHED_CAPACITY_SHIFT; > + delta = arch_scale_cpu_capacity(cpu) - __capacity; > + pr_debug("updating cpu%d thermal pressure to %lu\n", cpu, delta);
Surely we can do without the pr_debug() here?
> + per_cpu(delta_capacity, cpu) = delta; > +}
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