Messages in this thread | | | From | Vince Weaver <> | Date | Mon, 13 Mar 2017 09:58:00 -0400 (EDT) | Subject | perf: race with automatic rdpmc() disabling |
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Hello
I've been trying to track this issue down for a few days and haven't been able to isolate it. So maybe someone who understands low-level perf mmap reference counting can help here.
As you might recall, 7911d3f7af14a614617e38245fedf98a724e46a9 introduced automatic disabling of userspace rdpmc when no perf_events were running.
I've run into a problem with PAPI when using rdpmc. If you have PAPI measuring events in multiple pthread threads, sometimes (but not always) the program will GPF because CR4/rdpmc gets turned off while events are still active.
I've been trying to put together a reproducible test case but haven't been able to manage. I have a PAPI test that will show the problem about 50% of the time but I can't seem to isolate the problem.
Any ideas?
If you really want to try to reproduce it, get the current git version of PAPI git clone https://bitbucket.org/icl/papi.git edit src/components/perf_event/perf_event.c so that #define PERF_USE_RDPMC 1 in src run ./configure , make then run the ./ctests/zero_pthreads test a few times. It will GPF and I'm relatively (though not entirely) sure it's not a PAPI issue. The problem does go away if you set /sys/devices/cpu/rdpmc to 2
Vince
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