2018-01-24 17:14 GMT+08:00 Peter Zijlstra <[email protected]>: > On Wed, Jan 24, 2018 at 04:32:38PM +0800, Lin Xiulei wrote: >> >> 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. > > But that might still be too early, we might still have more cgroup > events active. > > What goes wrong if we leave it set? > >> 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() > > OK, I think I can see that happening. Please clarify the Changelog and > maybe put a comment in the code as well.
Sure, and I consider this "OK" works for "What goes wrong if we leave it set?". : )
