linux-kernel - Re: [PATCH] perf_counter: cleanup for __perf_event_sched

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Date:	Wed, 23 Sep 2009 10:45:04 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Paul Mackerras <paulus@...ba.org>
CC:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf_counter: cleanup for __perf_event_sched_in()



Paul Mackerras wrote:
> Xiao Guangrong writes:
> 
>> It must be a group leader if event->attr.pinned is "1"
> 
> 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.
> 

I only find three places in __perf_event_sched_in/out, could you tell me
where is the fourth place?

I also noticed that all group leader is the top level of ctx->group_list,
if I not missed, the perf_event_init_task() function can be optimized,
like this:

int perf_event_init_task(struct task_struct *child)
{
	......
	/* We can only look at parent_ctx->group_list to get group leader */
	list_for_each_entry_rcu(event, &parent_ctx->event_list, event_entry) {
		if (event != event->group_leader)
			continue;
	......
	}
	......
}

I'll fix those if you are not mind :-)

Thanks,
Xiao
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