linux-kernel - Re: [PATCH 2/2] perf: Disable the event on a truncated AUX record

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Message-ID: <20160511091333.GA3190@twins.programming.kicks-ass.net>
Date:	Wed, 11 May 2016 11:13:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org, vince@...ter.net, eranian@...gle.com,
	Arnaldo Carvalho de Melo <acme@...radead.org>
Subject: Re: [PATCH 2/2] perf: Disable the event on a truncated AUX record

On Tue, May 10, 2016 at 04:18:33PM +0300, Alexander Shishkin wrote:
> When the PMU driver reports a truncated AUX record, it effectively means
> that there is no more usable room in the event's AUX buffer (even though
> there may still be some room, so that perf_aux_output_begin() doesn't take
> action). At this point the consumer still has to be woken up and the event
> has to be disabled, otherwise the event will just keep spinning between
> perf_aux_output_begin() and perf_aux_output_end() until its context gets
> unscheduled.
> 
> Again, for cpu-wide events this means never, so once in this condition,
> they will be forever losing data.
> 
> Fix this by disabling the event and waking up the consumer in case of a
> truncated AUX record.

> +	if (wakeup) {
> +		if (truncated)
> +			handle->event->pending_disable = 1;
> +		perf_output_wakeup(handle);
> +	}

Does the userspace tool know how to deal with this and re-enable it?