linux-kernel - Re: [PATCH v3 7/8] perf: Define PMU_TXN

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Date:	Fri, 17 Jul 2015 00:20:15 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-s390@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH v3 7/8] perf: Define PMU_TXN_READ interface

On Tue, Jul 14, 2015 at 08:01:54PM -0700, Sukadev Bhattiprolu wrote:
> +/*
> + * Use the transaction interface to read the group of events in @leader.
> + * PMUs like the 24x7 counters in Power, can use this to queue the events
> + * in the ->read() operation and perform the actual read in ->commit_txn.
> + *
> + * Other PMUs can ignore the ->start_txn and ->commit_txn and read each
> + * PMU directly in the ->read() operation.
> + */
> +static int perf_event_read_group(struct perf_event *leader)
> +{
> +	int ret;
> +	struct perf_event *sub;
> +	struct pmu *pmu;
> +
> +	pmu = leader->pmu;
> +
> +	pmu->start_txn(pmu, PERF_PMU_TXN_READ);
> +
> +	perf_event_read(leader);

There should be a lockdep assert with that list iteration.

> +	list_for_each_entry(sub, &leader->sibling_list, group_entry)
> +		perf_event_read(sub);
> +
> +	ret = pmu->commit_txn(pmu);
> +
> +	return ret;
> +}
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