Messages in this thread | | | Date | Thu, 26 Jan 2023 12:42:01 +0100 | Subject | Re: [PATCH v4] sched/fair: unlink misfit task from cpu overutilized | From | Dietmar Eggemann <> |
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On 19/01/2023 17:42, Vincent Guittot wrote: > By taking into account uclamp_min, the 1:1 relation between task misfit > and cpu overutilized is no more true as a task with a small util_avg may > not fit a high capacity cpu because of uclamp_min constraint. > > Add a new state in util_fits_cpu() to reflect the case that task would fit > a CPU except for the uclamp_min hint which is a performance requirement. > > Use -1 to reflect that a CPU doesn't fit only because of uclamp_min so we > can use this new value to take additional action to select the best CPU > that doesn't match uclamp_min hint. > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > --- > > Change since v3: > - Keep current condition for uclamp_max_fits in util_fits_cpu() > - Update some comments
We had already this discussion whether this patch can also remove Capacity Inversion (CapInv).
After studying the code again, I'm not so sure anymore.
This patch:
(1) adds a dedicated return value (-1) to util_fits_cpu() when:
`util fits 80% capacity_of() && util < uclamp_min && uclamp_min > capacity_orig_thermal (region c)`
(2) Enhancements to the CPU selection in sic() and feec() to cater for this new return value.
IMHO this doesn't make the intention of CapInv in util_fits_cpu() obsolete, which is using:
in CapInv:
capacity_orig = capacity_orig_of() - thermal_load_avg capacity_orig_thermal = capacity_orig_of() - thermal_load_avg
not in CapInv:
capacity_orig = capacity_orig_of() capacity_orig_thermal = capacity_orig_of() - th_pressure
Maybe I still miss a bit of the story?
v3 hints to removing the bits in the next version:
https://lkml.kernel.org/r/20230115001906.v7uq4ddodrbvye7d@airbuntu
> kernel/sched/fair.c | 105 ++++++++++++++++++++++++++++++++++---------- > 1 file changed, 82 insertions(+), 23 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index d4db72f8f84e..54e14da53274 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4561,8 +4561,8 @@ static inline int util_fits_cpu(unsigned long util, > * handle the case uclamp_min > uclamp_max. > */ > uclamp_min = min(uclamp_min, uclamp_max); > - if (util < uclamp_min && capacity_orig != SCHED_CAPACITY_SCALE) > - fits = fits && (uclamp_min <= capacity_orig_thermal); > + if (fits && (util < uclamp_min) && (uclamp_min > capacity_orig_thermal)) > + return -1;
Or does the definition 'return -1 if util fits but uclamp doesn't' make the distinction between capacity_orig and capacity_orig_thermal obsolete and so CapInv?
[...]
> static inline void update_misfit_status(struct task_struct *p, struct rq *rq) > @@ -6138,6 +6142,7 @@ static inline bool cpu_overutilized(int cpu) > unsigned long rq_util_min = uclamp_rq_get(cpu_rq(cpu), UCLAMP_MIN); > unsigned long rq_util_max = uclamp_rq_get(cpu_rq(cpu), UCLAMP_MAX); > > + /* Return true only if the utilization doesn't fits CPU's capacity */
small typo: s/doesn't fits/doesn't fit
[...]
> @@ -6946,12 +6952,28 @@ select_idle_capacity(struct task_struct *p, struct sched_domain *sd, int target) > > if (!available_idle_cpu(cpu) && !sched_idle_cpu(cpu)) > continue; > - if (util_fits_cpu(task_util, util_min, util_max, cpu)) > + > + fits = util_fits_cpu(task_util, util_min, util_max, cpu); > + > + /* This CPU fits with all requirements */ > + if (fits > 0) > return cpu; > + /* > + * Only the min performance hint (i.e. uclamp_min) doesn't fit. > + * Look for the CPU with best capacity. > + */ > + else if (fits < 0) > + cpu_cap = capacity_orig_of(cpu) - thermal_load_avg(cpu_rq(cpu));
Still don't grasp why we use thermal_load_avg() here? Looks to me that this would only match the CapInv case in util_fits_cpu().
[...]
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