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From: Vince Weaver <vincent.weaver@maine.edu>
X-Google-Original-From: Vince Weaver <vince@vincent-weaver-1.umelst.maine.edu>
Date: Tue, 21 Jul 2015 14:14:54 -0400 (EDT)
To: linux-kernel@vger.kernel.org
cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: perf: multiplexing broken on amd fam16h?
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Hello

I have a new AMD A8 system and perf multiplexing support is acting weird.

If I run the perf_event_tests check_multiplexing test it fails like this:

Event	TotalCount	RawCount	Scale					ScaledCount	Error
0	500282143	150403975	-2.00 (c8050b5 fffffffff9c224ef)	-300807950	160.13%

So the problem is that the TOTAL_TIME_RUNNING value is negative, which as 
far as I know shouldn't be possible.  I can't seem to track down 
why this would happen, and the same kernel (4.2-rc3) running on a Haswell 
machine doesn't have this problem.

I tried to replicate the problem using perf, but for some reason I can't 
get perf to multiplex on any of my machines.  That used to transparently 
work didn't it?

here's the result on the haswell machine

perf stat -e cycles,instructions,cycles,instructions,cycles,instructions,cycles,instructions 
sleep 5

 Performance counter stats for 'sleep 5':

         1,354,527      cycles                   
         1,934,694      instructions              #    1.76  insns per cycle        
         1,521,148      cycles                   
         1,934,694      instructions              #    1.76  insns per cycle        
         1,521,148      cycles                   
         1,223,321      instructions              #    1.11  insns per cycle         [13.61%]
     <not counted>      cycles                   
     <not counted>      instructions             

       5.003651781 seconds time elapsed


Vince
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