linux-kernel - Re: [tip:perf/core] perf: Add group scheduling transactional APIs

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Date:	Mon, 10 May 2010 21:38:57 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...hat.com, hpa@...or.com, eranian@...gle.com,
	linux-kernel@...r.kernel.org, davem@...emloft.net,
	fweisbec@...il.com, ming.m.lin@...el.com, tglx@...utronix.de,
	mingo@...e.hu, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] perf: Add group scheduling transactional APIs

On Mon, May 10, 2010 at 10:11:55AM +0200, Peter Zijlstra wrote:

> Can't you compute n_txn_start by subtracting n_added from n_events ?

Well, n_added says how many have been added since hw_perf_disable, and
we could get multiple transactions inside a hw_perf_disable/enable
pair, if we're scheduling multiple groups on.  So n_events - n_added
doesn't tell us how many have been added in this transaction -- unless
I'm mistaken and there is a one transaction per hw_perf_disable/enable
rule, but I didn't see that written anywhere, and it does seem to be
explicitly one transaction per group.

Paul.
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