Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 18 Nov 2021 09:07:05 +0100 | Subject | Re: [PATCH] sched/fair: Replace CFS internal cpu_util() with cpu_util_cfs() |
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On Wed, 17 Nov 2021 at 18:26, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: > > On 12.11.21 17:20, Vincent Guittot wrote: > > On Fri, 12 Nov 2021 at 15:14, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: > >> > >> cpu_util_cfs() was created by commit d4edd662ac16 ("sched/cpufreq: Use > >> the DEADLINE utilization signal") to enable the access to CPU > >> utilization from the Schedutil CPUfreq governor. > >> > >> Commit a07630b8b2c1 ("sched/cpufreq/schedutil: Use util_est for OPP > >> selection") added util_est support later. > >> > >> The only thing cpu_util() is doing on top of what cpu_util_cfs() already > >> does is to clamp the return value to the [0..capacity_orig] capacity > >> range of the CPU. Integrating this into cpu_util_cfs() is not harming > >> the existing users (Schedutil and CPUfreq cooling (latter via > >> sched_cpu_util() wrapper)). > > > > Could you to update cpu_util_cfs() to use cpu as a parameter instead of rq ? > > I could but I decided to use use `struct rq *rq` instead. > > (A) We already know the rq in the following functions where we call > cpu_util_cfs():
The only user of cpu_util_cfs() is sugov_get_util() and it does cpu_util_cfs(cpu_rq(sg_cpu->cpu)) because rq is only used as a parameter of cpu_util_cfs()
all other ones are using cpu_util() which already uses cpu as a parameter so it's more straight forward to keep using cpu
> > update_sg_lb_stats() > find_busiest_queue() > update_numa_stats() > sugov_get_util() (existing cpu_util_cfs() call *) > > (B) For the following three functions we would call cpu_rq() outside > cpu_util_cfs(): > > cpu_overutilized() > cpu_util_without() > sched_cpu_util() (*) > > So for (A) we wouldn't call cpu_rq(cpu) twice, avoiding issues with the > RELOC_HIDE() thing in per_cpu(runqueues, cpu). > > > And cpu_util_cfs()'s PELT counterparts, cpu_load() and cpu_runnable() > also use rq. > > >> Remove cpu_util(). > >> > >> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> > >> --- > >> > >> I deliberately got rid of the comment on top of cpu_util(). It's from > >> the early days of using PELT utilization, it describes CPU utilization > >> behaviour before PELT time-scaling and talks about current capacity > >> which we don't maintain. > > > > would be good to keep an updated version in this case. There are lot > > of interesting informations in the comment > > Yes, can do. > > Something like this: > > /** > * cpu_util_cfs() - Estimates the amount of CPU capacity used by CFS tasks. > * @cpu: the CPU to get the utilization for.
cpu is clearly the right parameter ;-)
> * > * The unit of the return value must be the same as the one of CPU capacity > * so that CPU utilization can be compared with CPU capacity. > * > * CPU utilization is the sum of running time of runnable tasks plus the > * recent utilization of currently non-runnable tasks on that CPU. > * It represents the amount of CPU capacity currently used by CFS tasks in > * the range [0..max CPU capacity] with max CPU capacity being the CPU > * capacity at f_max. > * > * The estimated CPU utilization is defined as the maximum between CPU > * utilization and sum of the estimated utilization of the currently > * runnable tasks on that CPU. It preserves a utilization "snapshot" of > * previously-executed tasks, which helps better deduce how busy a CPU will > * be when a long-sleeping task wake up. Such task's contribution to CPU > * utilization would be decayed significantly at this point of time. > * > * CPU utilization can be higher than the current CPU capacity > * (f_curr/f_max * max CPU capacity) or even the max CPU capacity because > * of rounding errors as well as task migrations or wakeups of new tasks. > * CPU utilization has to be capped to fit into the [0..max CPU capacity] > * range. Otherwise a group of CPUs (CPU0 util = 121% + CPU1 util = 80%) > * could be seen as over-utilized even though CPU1 has 20% of spare CPU > * capacity. CPU utilization is allowed to overshoot current CPU capacity > * though since this is useful for predicting the CPU capacity required > * after task migrations (scheduler-driven DVFS). > * > * Return: (Estimated) utilization for the specified CPU. > */ > > [...]
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