Hello Vincent. On Fri, Feb 24, 2023 at 10:34:52AM +0100, Vincent Guittot <vincent.guittot@xxxxxxxxxx> wrote: > + cpu.latency.nice > + A read-write single value file which exists on non-root > + cgroups. The default is "0". > + > + The nice value is in the range [-20, 19]. > + > + This interface file allows reading and setting latency using the > + same values used by sched_setattr(2). The latency_nice of a group is > + used to limit the impact of the latency_nice of a task outside the > + group. IIUC, the latency priority is taken into account when deciding between entitites at the same level (as in pick_next_entity() or check_preempt_wake()/find_matchig_se()). So this group attribute is relevant in context of siblings (i.e. like cpu.weight ~ bandwidth priority)? I'm thus confused when it's referred to as a limit (in vertical sense). You somewhat imply that in [1]: > Regarding the behavior, the rule remains the same that a sched_entity > attached to a cgroup will not get more (latency in this case) than > what has been set for the group entity. But I don't see where such a constraint would be implemented in the code. (My cursory understanding above tends to horizontal comparisons.) Could you please hint me which is right? Thanks, Michal [1] https://lore.kernel.org/r/CAKfTPtDu=c-psGnHkoWSPRWoh1Z0VBBfsN++g+krv4B1SJmFjg@xxxxxxxxxxxxxx/
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