Re: [PATCH v2 net-next] bpf: fix bpf_perf_event_read() helper

[Wangnan (F)]

On 2015/10/22 13:00, Alexei Starovoitov wrote:
> On 10/21/15 9:49 PM, Wangnan (F) wrote:
> > After applying this patch I'm unable to use perf passing perf_event
> > again like this:
>
> please do not top post and trim your replies.
>
> >   # perf record -a -e evt=cycles -e
> > ./test_config_map.c/maps.pmu_map.event=evt/ --exclude-perf ls
> >
> > With -v it output:
> >
> > ...
> > adding perf_bpf_probe:func_write
> > adding perf_bpf_probe:func_write to 0x367d6a0
> > add bpf event perf_bpf_probe:func_write_return and attach bpf program 6
> > adding perf_bpf_probe:func_write_return
> > adding perf_bpf_probe:func_write_return to 0x3a7fc40
> > mmap size 528384B
> > ERROR: failed to insert value to pmu_map[0]
> > ERROR: Apply config to BPF failed: Invalid option for map, add -v to see
> > detail
> > Opening /sys/kernel/debug/tracing//kprobe_events write=
> > ...
> >
> > Looks like perf sets attr.inherit for cycles? I'll look into this 
> > problem.
>
> yes. that's perf default.
> How did it even work before?!
> I was testing with your samples/bpf/tracex6 that sets inherit to zero.

Tested perf record -i option and it works for me:

# echo "" > /sys/kernel/debug/tracing/trace
# perf record -i -a -e evt=cycles -e 
./test_config_map.c/maps.pmu_map.event=evt/ --exclude-perf ls
# cat /sys/kernel/debug/tracing/trace  | grep ls
              ls-8227  [001] dN..  2526.184611: : pmu inc: 82270
              ls-8227  [001] dN..  2526.184626: : pmu inc: 40951
              ls-8227  [001] dN..  2526.184642: : pmu inc: 50659
              ls-8227  [001] dN..  2526.184657: : pmu inc: 43511
              ls-8227  [001] dN..  2526.184675: : pmu inc: 56921
...
And no warning message found in dmesg.

So I think your fix is good, we should improve perf.

Thank you.




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