Re: [PATCH v2 05/19] perf, tools: Support weak groups

[Jiri Olsa]

On Fri, Aug 11, 2017 at 04:26:20PM -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> 
> 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@krava 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