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Date: Tue, 22 Aug 2017 10:36:08 +0200 From: Jiri Olsa <jolsa@...hat.com> To: Andi Kleen <andi@...stfloor.org> Cc: acme@...nel.org, jolsa@...nel.org, linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com> Subject: Re: [PATCH v2 05/19] perf, tools: Support weak groups On Fri, Aug 11, 2017 at 04:26:20PM -0700, Andi Kleen wrote: > From: Andi Kleen <ak@...ux.intel.com> > > Setting up groups can be complicated due to the > complicated scheduling restrictions of different PMUs. > User tools usually don't understand all these restrictions. > Still in many cases it is useful to set up groups and > they work most of the time. However if the group > is set up wrong some members will not reported any values > because they never get scheduled. > > Add a concept of a 'weak group': try to set up a group, > but if it's not schedulable fallback to not using > a group. That gives us the best of both worlds: > groups if they work, but still a usable fallback if they don't. > > In theory it would be possible to have more complex fallback > strategies (e.g. try to split the group in half), but > the simple fallback of not using a group seems to work for now. > > So far the weak group is only implemented for perf stat, > not for record. > > Here's an unschedulable group (on IvyBridge with SMT on) > > % perf stat -e '{branches,branch-misses,l1d.replacement,l2_lines_in.all,l2_rqsts.all_code_rd}' -a sleep 1 > > 73,806,067 branches > 4,848,144 branch-misses # 6.57% of all branches > 14,754,458 l1d.replacement > 24,905,558 l2_lines_in.all > <not supported> l2_rqsts.all_code_rd <------- will never report anything also if I put 'cycles' instead of the l2_rqsts.all_code_rd, I get clean open but 'not counted' as result.. I wonder there's some counter scheduling issue [root@...va perf]# ./perf stat -v -e '{branches,branch-misses,l1d.replacement,l2_lines_in.all,cycles}:W' -a sleep 1 Using CPUID GenuineIntel-6-3D l1d.replacement -> cpu/umask=0x1,period=2000003,event=0x51/ l2_lines_in.all -> cpu/umask=0x7,period=100003,event=0xf1/ branches: 0 4004293853 0 branch-misses: 0 4004293853 0 l1d.replacement: 0 4004293853 0 l2_lines_in.all: 0 4004293853 0 cycles: 0 4004293853 0 Performance counter stats for 'system wide': <not counted> branches (0.00%) <not counted> branch-misses (0.00%) <not counted> l1d.replacement (0.00%) <not counted> l2_lines_in.all (0.00%) <not counted> cycles (0.00%) 1.001088589 seconds time elapsed jirka
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