Date: Mon, 11 Jan 2010 09:04:40 +1100
From: Paul Mackerras <paulus@samba.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
       Peter Zijlstra <peterz@infradead.org>,
       Arnaldo Carvalho de Melo <acme@redhat.com>
Subject: Re: [PATCH 6/6] perf: Increase round-robin fairness of flexible
 events
Message-ID: <20100110220440.GA4595@brick.ozlabs.ibm.com>
References: <1263087500-14215-1-git-send-regression-fweisbec@gmail.com>
 <1263087500-14215-7-git-send-regression-fweisbec@gmail.com>
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Frederic,

Nice to see someone working on the event scheduling in perf.

But I don't think this patch makes sense:

> Group of flexible events are round-robined in each tick so that
> each group has its chance to be scheduled. But the fairness
> per group granularity doesn't propagate inside the groups
> themselves.
> 
> If only the first events of each groups have a chance to make
> their way, the remaining ones will never be scheduled.
> 
> Hence this patch propagates the round-robin to the events
> inside the groups.

The semantic of a group is that either all of the events in the group
are scheduled in, or none of them are.  So it doesn't make sense to
talk about fairness within a group, and I don't see any point to
rotating the elements of the sibling_list.  Or have I misunderstood
what you're aiming at?

Paul.
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