Messages in this thread Patch in this message | | | Subject | Re: [PATCH 1/2] perf_counter: cleanup for __perf_event_sched_*() | From | Peter Zijlstra <> | Date | Wed, 23 Sep 2009 10:40:30 +0200 |
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On Wed, 2009-09-23 at 16:10 +0800, Xiao Guangrong wrote: > Paul Mackerras says: > > "Actually, looking at this more closely, it has to be a group leader > anyway since it's at the top level of ctx->group_list. In fact I see > four places where we do: > > list_for_each_entry(event, &ctx->group_list, group_entry) { > if (event == event->group_leader) > ... > > or the equivalent, three of which appear to have been introduced by > afedadf2 ("perf_counter: Optimize sched in/out of counters") back in > May by Peter Z. > > As far as I can see the if () is superfluous in each case (a singleton > event will be a group of 1 and will have its group_leader pointing to > itself)." > > [Can be found at http://marc.info/?l=linux-kernel&m=125361238901442&w=2] > > So, this patch fix it.
Hrm.. I think its not just a cleanup, but an actual bugfix.
The intent was to call event_sched_{in,out}() for single counter groups because that's cheaper than group_sched_{in,out}(), however..
- as you noticed, I got the condition wrong, it should have read:
list_empty(&event->sibling_list)
- it failed to call group_can_go_on() which deals with ->exclusive.
- it also doesn't call hw_perf_group_sched_in() which might break power.
Also, I'm not sure I like the comments and WARN_ON bits, the changelog should be sufficient.
> Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com> > --- > kernel/perf_event.c | 41 +++++++++++++++++++++++------------------ > 1 files changed, 23 insertions(+), 18 deletions(-) > > diff --git a/kernel/perf_event.c b/kernel/perf_event.c > index 76ac4db..9ca975a 100644 > --- a/kernel/perf_event.c > +++ b/kernel/perf_event.c > @@ -1032,10 +1032,13 @@ void __perf_event_sched_out(struct perf_event_context *ctx, > perf_disable(); > if (ctx->nr_active) { > list_for_each_entry(event, &ctx->group_list, group_entry) { > - if (event != event->group_leader) > - event_sched_out(event, cpuctx, ctx); > - else > - group_sched_out(event, cpuctx, ctx); > + > + /* > + * It has to be a group leader since it's at the top > + * level of ctx->group_list > + */ > + WARN_ON_ONCE(event != event->group_leader); > + group_sched_out(event, cpuctx, ctx); > } > } > perf_enable(); > @@ -1258,12 +1261,14 @@ __perf_event_sched_in(struct perf_event_context *ctx, > if (event->cpu != -1 && event->cpu != cpu) > continue; > > - if (event != event->group_leader) > - event_sched_in(event, cpuctx, ctx, cpu); > - else { > - if (group_can_go_on(event, cpuctx, 1)) > - group_sched_in(event, cpuctx, ctx, cpu); > - } > + /* > + * It has to be a group leader since it's at the top > + * level of ctx->group_list > + */ > + WARN_ON_ONCE(event != event->group_leader); > + > + if (group_can_go_on(event, cpuctx, 1)) > + group_sched_in(event, cpuctx, ctx, cpu); > > /* > * If this pinned group hasn't been scheduled, > @@ -1291,15 +1296,15 @@ __perf_event_sched_in(struct perf_event_context *ctx, > if (event->cpu != -1 && event->cpu != cpu) > continue; > > - if (event != event->group_leader) { > - if (event_sched_in(event, cpuctx, ctx, cpu)) > + /* > + * It has to be a group leader since it's at the top > + * level of ctx->group_list > + */ > + WARN_ON_ONCE(event != event->group_leader); > + > + if (group_can_go_on(event, cpuctx, can_add_hw)) > + if (group_sched_in(event, cpuctx, ctx, cpu)) > can_add_hw = 0; > - } else { > - if (group_can_go_on(event, cpuctx, can_add_hw)) { > - if (group_sched_in(event, cpuctx, ctx, cpu)) > - can_add_hw = 0; > - } > - } > } > perf_enable(); > out:
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