linux-kernel - Re: [PATCH v3 1/7] perf: Allow normal events to be sources of AUX data

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Message-ID: <20190731162106.GX31381@hirez.programming.kicks-ass.net>
Date:   Wed, 31 Jul 2019 18:21:06 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        kan.liang@...ux.intel.com
Subject: Re: [PATCH v3 1/7] perf: Allow normal events to be sources of AUX
 data

On Wed, Jul 31, 2019 at 05:30:35PM +0300, Alexander Shishkin wrote:
> +static void perf_put_aux_event(struct perf_event *event)
> +{
> +	struct perf_event_context *ctx = event->ctx;
> +	struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
> +	struct perf_event *iter = NULL;
> +
> +	/*
> +	 * If event uses aux_event tear down the link
> +	 */
> +	if (event->aux_event) {
> +		put_event(event->aux_event);
> +		event->aux_event = NULL;

Those lines should probably be reversed; put_event() should be done
after clearing the link.

It probably doesn't matter, but it is confusing.

> +		return;
> +	}
> +
> +	/*
> +	 * If the event is an aux_event, tear down all links to
> +	 * it from other events.
> +	 */
> +	for_each_sibling_event(iter, event->group_leader) {
> +		if (iter->aux_event != event)
> +			continue;
> +
> +		iter->aux_event = NULL;
> +		put_event(event);
> +
> +		/*
> +		 * If it's ACTIVE, schedule it out. It won't schedule
> +		 * again because !aux_event.
> +		 */
> +		event_sched_out(iter, cpuctx, ctx);
> +	}
> +}