linux-kernel - Re: [PATCH] perf_events: fix and improve x86 event scheduling

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Message-ID: <1320677770.18053.51.camel@twins>
Date:	Mon, 07 Nov 2011 15:56:10 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, robert.richter@....com,
	mingo@...e.hu, ming.m.lin@...el.com, ak@...ux.intel.com
Subject: Re: [PATCH] perf_events: fix and improve x86 event scheduling

On Mon, 2011-11-07 at 13:52 +0000, Stephane Eranian wrote:
> But given we limit the number of events to that of counters,
> we do have O(c^3). 

Right, but SNB without HT gives you 8 GP counters, yielding a rather big
number. Suppose you're trying to fill it with 9 cycle events (1 for the
fixed purpose thingy), that'll end up being: 9^3 = 729 = big number.

(arguably adding 9 cycle counters is a tad retarded, but hey ;-)

It would be good to try and get it down to somewhere near 81 again,
although my brain isn't currently providing any sane ideas on how.

> As for the map_idx, it's there to track the position of each event in the
> initial event list. We shuffle events between constrained and unconstrained.
> By stashing the map_idx in the hw_perf_event struct we avoid having to
> pass around yet another array.

Yeah, I saw why you needed it..
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