From: Vince Weaver <vincent.weaver@maine.edu>
To: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: perf: rdpmc mmap page time_enabled issue
Date: Tue, 14 Mar 2017 23:41:10 -0400 (EDT) [thread overview]
Message-ID: <alpine.DEB.2.20.1703142321360.29558@macbook-air> (raw)
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
next reply other threads:[~2017-03-15 3:41 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-15 3:41 Vince Weaver [this message]
2017-03-17 14:37 ` perf: negative " Vince Weaver
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