linux-kernel - Re: [PATCH V6 11/14] perf/x86/intel: Disable sample-read the slots and metrics events

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Message-ID: <20200721191811.GH10769@hirez.programming.kicks-ass.net>
Date:   Tue, 21 Jul 2020 21:18:11 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     acme@...hat.com, mingo@...nel.org, linux-kernel@...r.kernel.org,
        jolsa@...nel.org, eranian@...gle.com,
        alexander.shishkin@...ux.intel.com, ak@...ux.intel.com
Subject: Re: [PATCH V6 11/14] perf/x86/intel: Disable sample-read the slots
 and metrics events

On Tue, Jul 21, 2020 at 12:07:29PM -0400, Liang, Kan wrote:

> I'm trying to produce the bug mentioned above, but I'm not sure under what
> situation, the core code will 'promote' the sibling metric events?

Create an event group:

	fd = sys_perf_event_open();
	fd1 = sys_perf_event_open(.group_fd = fd);
	...

then kill the group leader:

	close(fd);

Then the sibling events: fdN, should get promoted. Ideally try and use
fd1 in a read or so after this.

> I tried the suggested code below. It works well for the sample-read case.
> Perf tool errors out as expected.

I'm not sure you can create that case with perf-tool, it's a bit of a
daft thing to do, so you'll have to write a custom program.