perf: rdpmc mmap page time_enabled issue

From	Vince Weaver <vincent.weaver@maine.edu>
Newsgroups	linux.kernel
Subject	perf: rdpmc mmap page time_enabled issue
Date	2017-03-15 04:50 +0100
Message-ID	<tl86J-1Jb-9@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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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

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perf: rdpmc mmap page time_enabled issue Vince Weaver <vincent.weaver@maine.edu> - 2017-03-15 04:50 +0100
  Re: perf: negative time_enabled issue Vince Weaver <vincent.weaver@maine.edu> - 2017-03-17 15:40 +0100

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