On 04/02/2021 12:34, Valentin Schneider wrote: > On 04/02/21 11:49, Dietmar Eggemann wrote: >> On 03/02/2021 16:15, Qais Yousef wrote: >>> On 01/28/21 18:31, Valentin Schneider wrote:
[...] > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 21bd71f58c06..ea7f0155e268 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1482,6 +1482,33 @@ DECLARE_PER_CPU(struct sched_domain __rcu *, > sd_asym_packing); > DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity); > extern struct static_key_false sched_asym_cpucapacity; > > +/* > + * Note that the static key is system-wide, but the visibility of > + * SD_ASYM_CPUCAPACITY isn't. Thus the static key being enabled does not > + * imply all CPUs can see asymmetry. > + * > + * Consider an asymmetric CPU capacity system such as: > + * > + * MC [ ] > + * 0 1 2 3 4 5 > + * L L L L B B > + * > + * w/ arch_scale_cpu_capacity(L) < arch_scale_cpu_capacity(B) > + * > + * By default, booting this system will enable the sched_asym_cpucapacity > + * static key, and all CPUs will see SD_ASYM_CPUCAPACITY set at their MC > + * sched_domain. > + * > + * Further consider exclusive cpusets creating a "symmetric island": > + * > + * MC [ ][ ] > + * 0 1 2 3 4 5 > + * L L L L B B > + * > + * Again, booting this will enable the static key, but CPUs 0-1 will *not* > have > + * SD_ASYM_CPUCAPACITY set in any of their sched_domain. This is the > intending s/intending/intended > + * behaviour, as CPUs 0-1 should be treated as a regular, isolated SMP > system. > + */ LGTM.
