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

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Message-ID: <19128.39768.149110.673711@cargo.ozlabs.ibm.com>
Date:	Tue, 22 Sep 2009 19:39:36 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
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()

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.

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).  Peter, do you agree or have I missed something?

Paul.
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