Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 17 Oct 2019 10:44:54 +0200 | Subject | Re: [Patch v3 2/7] sched: Add infrastructure to store and update instantaneous thermal pressure |
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Hi Thara,
On Wed, 16 Oct 2019 at 23:22, Thara Gopinath <thara.gopinath@linaro.org> wrote: > > Hi Vincent, > > Thanks for the review > On 10/14/2019 11:50 AM, Vincent Guittot wrote: > > Hi Thara, > > > > On Mon, 14 Oct 2019 at 02:58, Thara Gopinath <thara.gopinath@linaro.org> 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 structure max_capacity_info is > >> introduced to keep track of instantaneous per cpu thermal pressure. > >> Thermal pressure is the delta between max_capacity and cap_capacity. > >> API update_periodic_maxcap is called for periodic accumulate and decay > >> of the thermal pressure. It is to to be called from a periodic tick > >> function. This API calculates the delta between max_capacity and > >> cap_capacity and passes on the delta to update_thermal_avg to do the > >> necessary accumulate, decay and average. API update_maxcap_capacity is for > >> the system to update the thermal pressure by updating cap_capacity. > >> Considering, update_periodic_maxcap reads cap_capacity and > >> update_maxcap_capacity writes into cap_capacity, one can argue for > >> some sort of locking mechanism to avoid a stale value. > >> But considering update_periodic_maxcap 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 value used to > >> calculate average thermal pressure for a cpu can be stale for upto 1 > >> tick period. > >> > >> Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org> > >> --- > >> include/linux/sched.h | 14 +++++++++++ > >> kernel/sched/Makefile | 2 +- > >> kernel/sched/thermal.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++ > >> kernel/sched/thermal.h | 13 ++++++++++ > >> 4 files changed, 94 insertions(+), 1 deletion(-) > >> create mode 100644 kernel/sched/thermal.c > >> create mode 100644 kernel/sched/thermal.h > >> > >> diff --git a/include/linux/sched.h b/include/linux/sched.h > >> index 2c2e56b..875ce2b 100644 > >> --- a/include/linux/sched.h > >> +++ b/include/linux/sched.h > >> @@ -1983,6 +1983,20 @@ static inline void rseq_syscall(struct pt_regs *regs) > >> > >> #endif > >> > >> +#ifdef CONFIG_SMP > >> +void update_maxcap_capacity(int cpu, u64 capacity); > >> + > >> +void populate_max_capacity_info(void); > >> +#else > >> +static inline void update_maxcap_capacity(int cpu, u64 capacity) > >> +{ > >> +} > >> + > >> +static inline void populate_max_capacity_info(void) > >> +{ > >> +} > >> +#endif > >> + > >> const struct sched_avg *sched_trace_cfs_rq_avg(struct cfs_rq *cfs_rq); > >> char *sched_trace_cfs_rq_path(struct cfs_rq *cfs_rq, char *str, int len); > >> int sched_trace_cfs_rq_cpu(struct cfs_rq *cfs_rq); > >> diff --git a/kernel/sched/Makefile b/kernel/sched/Makefile > >> index 21fb5a5..4d3b820 100644 > >> --- a/kernel/sched/Makefile > >> +++ b/kernel/sched/Makefile > >> @@ -20,7 +20,7 @@ obj-y += core.o loadavg.o clock.o cputime.o > >> obj-y += idle.o fair.o rt.o deadline.o > >> obj-y += wait.o wait_bit.o swait.o completion.o > >> > >> -obj-$(CONFIG_SMP) += cpupri.o cpudeadline.o topology.o stop_task.o pelt.o > >> +obj-$(CONFIG_SMP) += cpupri.o cpudeadline.o topology.o stop_task.o pelt.o thermal.o > >> obj-$(CONFIG_SCHED_AUTOGROUP) += autogroup.o > >> obj-$(CONFIG_SCHEDSTATS) += stats.o > >> obj-$(CONFIG_SCHED_DEBUG) += debug.o > >> diff --git a/kernel/sched/thermal.c b/kernel/sched/thermal.c > >> new file mode 100644 > >> index 0000000..5f0b2d4 > >> --- /dev/null > >> +++ b/kernel/sched/thermal.c > >> @@ -0,0 +1,66 @@ > >> +// SPDX-License-Identifier: GPL-2.0 > >> +/* > >> + * Sceduler 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" > >> + > >> +struct max_capacity_info { > >> + unsigned long max_capacity; > >> + unsigned long cap_capacity; > >> +}; > >> + > >> +static DEFINE_PER_CPU(struct max_capacity_info, max_cap); > >> + > >> +void update_maxcap_capacity(int cpu, u64 capacity) > >> +{ > >> + struct max_capacity_info *__max_cap; > >> + unsigned long __capacity; > >> + > >> + __max_cap = (&per_cpu(max_cap, cpu)); > >> + if (!__max_cap) { > >> + pr_err("no max_capacity_info structure for cpu %d\n", cpu); > >> + return; > >> + } > >> + > >> + /* Normalize the capacity */ > >> + __capacity = (capacity * arch_scale_cpu_capacity(cpu)) >> > >> + SCHED_CAPACITY_SHIFT; > >> + pr_debug("updating cpu%d capped capacity from %lu to %lu\n", cpu, __max_cap->cap_capacity, __capacity); > >> + > >> + __max_cap->cap_capacity = __capacity; > >> +} > >> + > >> +void populate_max_capacity_info(void) > >> +{ > >> + struct max_capacity_info *__max_cap; > >> + u64 capacity; > >> + int cpu; > >> + > >> + for_each_possible_cpu(cpu) { > >> + __max_cap = (&per_cpu(max_cap, cpu)); > >> + if (!__max_cap) > >> + continue; > >> + capacity = arch_scale_cpu_capacity(cpu); > >> + __max_cap->max_capacity = capacity; > >> + __max_cap->cap_capacity = capacity; > >> + pr_debug("cpu %d max capacity set to %ld\n", cpu, __max_cap->max_capacity); > >> + } > >> +} > > > > everything above seems to be there for the cpu cooling device and > > should be included in it instead. The scheduler only need the capacity > > capping > > The cpu cooling device should just set the delta capacity in the > > per-cpu variable (see my comment below) > It can be a firmware updating the thermal pressure instead of cpu > cooling device. Or may be some other entity .So instead of replicating > this code, isnt't it better to reside in one place ?
But you have now idea which kind of metrics will be provided by firmware. It might not be a capped frequency and a max frequency but other metrics. Also, __max_cap->max_capacity just save in a new per cpu struct the return of arch_scale_cpu_capacity but this doesn't give us real benefit
> > > >> + > >> +void update_periodic_maxcap(struct rq *rq) > >> +{ > >> + struct max_capacity_info *__max_cap = (&per_cpu(max_cap, cpu_of(rq))); > >> + unsigned long delta; > >> + > >> + if (!__max_cap) > >> + return; > >> + > >> + delta = __max_cap->max_capacity - __max_cap->cap_capacity; > > > > Why don't you just save the delta in the per_cpu variable instead of > > the struct max_capacity_info ? You have to compute the delta every > > tick whereas we can expect it to not change that much compared to the > > number of tick. > > Again I think thermal pressure can be applied from other entities like > firmware as well. But I agree with your point that calculating delta > every tick is not a good idea. How about I move it to > update_maxcap_capacity so that delta is calculate every time an update > comes from cpu cooling device or anybody else ? > > Warm Regards > Thara >
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