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During load-balance, groups classified as group_misfit_task are filtered out if they do not pass group_smaller_max_cpu_capacity(<candidate group>, <local group>); which itself employs fits_capacity() to compare the sgc->max_capacity of both groups. Due to the underlying margin, fits_capacity(X, 1024) will return false for any X > 819. Tough luck, the capacity_orig's on e.g. the Pixel 4 are {261, 871, 1024}. If a CPU-bound task ends up on one of those "medium" CPUs, misfit migration will never intentionally upmigrate it to a CPU of higher capacity due to the aforementioned margin. One may argue the 20% margin of fits_capacity() is excessive in the advent of counter-enhanced load tracking (APERF/MPERF, AMUs), but one point here is that fits_capacity() is meant to compare a utilization value to a capacity value, whereas here it is being used to compare two capacity values. As CPU capacity and task utilization have different dynamics, a sensible approach here would be to add a new helper dedicated to comparing CPU capacities. Also note that comparing capacity extrema of local and source sched_group's doesn't make much sense when at the day of the day the imbalance will be pulled by a known env->dst_cpu, whose capacity can be anywhere within the local group's capacity extrema. While at it, replace group_smaller_{min, max}_cpu_capacity() with comparisons of the source group's min/max capacity and the destination CPU's capacity. Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Reviewed-by: Qais Yousef <qais.yousef@arm.com> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> Tested-by: Lingutla Chandrasekhar <clingutla@codeaurora.org> Link: https://lkml.kernel.org/r/20210407220628.3798191-4-valentin.schneider@arm.com |
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.. | ||
autogroup.c | ||
autogroup.h | ||
clock.c | ||
completion.c | ||
core.c | ||
cpuacct.c | ||
cpudeadline.c | ||
cpudeadline.h | ||
cpufreq.c | ||
cpufreq_schedutil.c | ||
cpupri.c | ||
cpupri.h | ||
cputime.c | ||
deadline.c | ||
debug.c | ||
fair.c | ||
features.h | ||
idle.c | ||
isolation.c | ||
loadavg.c | ||
Makefile | ||
membarrier.c | ||
pelt.c | ||
pelt.h | ||
psi.c | ||
rt.c | ||
sched-pelt.h | ||
sched.h | ||
smp.h | ||
stats.c | ||
stats.h | ||
stop_task.c | ||
swait.c | ||
topology.c | ||
wait.c | ||
wait_bit.c |