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From: Vince Weaver <vincent.weaver@maine.edu>
X-Google-Original-From: Vince Weaver <vince@maine.edu>
Date: Wed, 17 Aug 2016 00:53:01 -0400 (EDT)
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To: linux-kernel@vger.kernel.org
cc: Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: perf: rdpmc and PERF_EVENT_IOC_RESET
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Hello

so using rdpmc() and the mmap page to do fast perf_event reads seems to 
interact poorly with the PERF_EVENT_IOC_RESET ioctl.

>>From what I can tell, on reset event->count is set to zero, but 
event->hw.prev_count is not, so the userpg->offset field ends up negative 
and weird things happen.

Shout reset just not be called if you are using the rdpmc() interface?

Vince