On Thu, Aug 31, 2017 at 12:40:26PM -0700, Andi Kleen wrote: > From: Andi Kleen <[email protected]> > > 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 > > With the weak group: > > % perf stat -e > '{branches,branch-misses,l1d.replacement,l2_lines_in.all,l2_rqsts.all_code_rd}:W' > -a sleep 1 > > 125,366,055 branches > (80.02%) > 9,208,402 branch-misses # 7.35% of all branches > (80.01%) > 24,560,249 l1d.replacement > (80.00%) > 43,174,971 l2_lines_in.all > (80.05%) > 31,891,457 l2_rqsts.all_code_rd > (79.92%) > > The extra event scheduled with some extra multiplexing > > v2: Move fallback code to separate function. > Add comment on for_each_group_member > Adjust to new perf_evsel__close interface > v3: > Fix debug print out. > Signed-off-by: Andi Kleen <[email protected]>
Acked-by: Jiri Olsa <[email protected]> thanks, jirka
