2018-01-24 16:20 GMT+08:00 Peter Zijlstra <[email protected]>: > On Wed, Jan 24, 2018 at 03:50:10PM +0800, [email protected] wrote: >> From: "leilei.lin" <[email protected]> >> >> Do not install cgroup event into the CPU context if the cgroup >> is not running on this CPU >> >> While there is no task of cgroup running specified CPU, current >> kernel still install cgroup event into CPU context, that causes >> another cgroup event can't be installed into this CPU. > > This changelog doesn't really cover the extend of the changes done. >
See below please > >> Signed-off-by: leilei.lin <[email protected]> >> --- >> kernel/events/core.c | 44 +++++++++++++++++++++++++++++++------------- >> 1 file changed, 31 insertions(+), 13 deletions(-) >> >> diff --git a/kernel/events/core.c b/kernel/events/core.c >> index 4df5b69..f766b60 100644 >> --- a/kernel/events/core.c >> +++ b/kernel/events/core.c >> @@ -933,31 +933,36 @@ list_update_cgroup_event(struct perf_event *event, >> { >> struct perf_cpu_context *cpuctx; >> struct list_head *cpuctx_entry; >> + struct perf_cgroup *cgrp; >> >> if (!is_cgroup_event(event)) >> return; >> >> /* >> * Because cgroup events are always per-cpu events, >> * this will always be called from the right CPU. >> */ >> cpuctx = __get_cpu_context(ctx); >> + cgrp = perf_cgroup_from_task(current, ctx); >> >> + /* cpuctx->cgrp is NULL unless a cgroup event is running in this CPU >> .*/ >> + if (cgroup_is_descendant(cgrp->css.cgroup, event->cgrp->css.cgroup)) { >> + if (add) >> cpuctx->cgrp = cgrp; >> + else >> + cpuctx->cgrp = NULL; >> } >> + >> + if (add && ctx->nr_cgroups++) >> + return; >> + else if (!add && --ctx->nr_cgroups) >> + return; >> + >> + cpuctx_entry = &cpuctx->cgrp_cpuctx_entry; >> + if (add) >> + list_add(cpuctx_entry, this_cpu_ptr(&cgrp_cpuctx_list)); >> + else >> + list_del(cpuctx_entry); >> } > > I'm a little confused; you unconditionally set cpuctx->cgrp for every > add/delete. > > So if we have >1 cgroup events on, and we remove one, you still clear > cpuctx->cgrp, that seems wrong. > > Why did you change that? The Changelog doesn't include enough clues for > me to know what you were trying to do. if we have > 1 cgroup events on, whenever a cgroup was really to be deleted, only if this cgroup is the same as the cgroup running on this cpu, I would clear cpuctx->cgrp. Reverse is the same. Here is the problem, previous version didn't set cpuctx->cgrp anymore if ctx->nr_cgroups > 1, which cases a second event would not be activated immediately because cpuctx->cgrp isn't equal to event->cgrp at event_filter_match()
