linux-kernel - perf: rdpmc mmap page time

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Message-ID: <alpine.DEB.2.20.1703142321360.29558@macbook-air>
Date:   Tue, 14 Mar 2017 23:41:10 -0400 (EDT)
From:   Vince Weaver <vincent.weaver@...ne.edu>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: perf: rdpmc mmap page time_enabled issue


So another obscure rdpmc problem, turned up by the PAPI regression tests.

If you use rdpmc, and your event is attached measuring another process,
and then you ENABLE/DISABLE/ENABLE/rdpmc the event

somehow the userpg->time_enabled field gets a weird value and that 
completely confuses code expecting enabled!=running to mean multiplexing 
is happening.

Example:

Trying attach:
	* RDPMC 1 Event 0 -- count: 1058381 enabled ffe6935332c70240 running: 9d14f
	* RDPMC 1 Event 1 -- count: 623980 enabled ffe6935332c829b3 running: 9d350

the rdpmc count and running values are expected, but the enabled value is way 
off, it should match the running value.

If you want to test this out, I have a test case in perf_event_tests, 
(github.com/deater/perf_event_tests.git)
	tests/rdpmc/rdpmc_multiattach_papi

Vince