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 <[email protected]> > 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 <[email protected]> >> --- >> 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 >> <[email protected]> >> + */ >> + >> +#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 ? > >> + >> +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
