Re: [PATCH 10/48] perf tools: Introduce bpf-output event

[Wangnan (F)]

On 2016/2/24 9:58, Wangnan (F) wrote:
> On 2016/2/24 1:45, Arnaldo Carvalho de Melo wrote:
> > Em Mon, Feb 22, 2016 at 09:10:37AM +0000, Wang Nan escreveu:
> > > Commit a43eec304259a6c637f4014a6d4767159b6a3aa3 (bpf: introduce
> > > bpf_perf_event_output() helper) add a helper to enable BPF program
> > > output data to perf ring buffer through a new type of perf event
> > > PERF_COUNT_SW_BPF_OUTPUT. This patch enable perf to create perf
> > > event of that type. Now perf user can use following cmdline to
> > > receive output data from BPF programs:
> > >
> > >   # ./perf record -a -e bpf-output/no-inherit,name=evt/ \
> > >                      -e ./test_bpf_output.c/map:channel.event=evt/ ls /
> > >   # ./perf script
> > >              perf  1560 [004] 347747.086295:                       
> > > evt:  ffffffff811fd201 sys_write ...
> > >              perf  1560 [004] 347747.086300:                       
> > > evt:  ffffffff811fd201 sys_write ...
> > >              perf  1560 [004] 347747.086315:                       
> > > evt:  ffffffff811fd201 sys_write ...
> > >              ...
> > >
> > > Test result:
> > >   # cat ./test_bpf_output.c
> > >   /************************ BEGIN **************************/
> > >   #include <uapi/linux/bpf.h>
> > >   struct bpf_map_def {
> > >       unsigned int type;
> > >       unsigned int key_size;
> > >       unsigned int value_size;
> > >       unsigned int max_entries;
> > >   };
> > >
> > >   #define SEC(NAME) __attribute__((section(NAME), used))
> > >   static u64 (*ktime_get_ns)(void) =
> > >       (void *)BPF_FUNC_ktime_get_ns;
> > >   static int (*trace_printk)(const char *fmt, int fmt_size, ...) =
> > >       (void *)BPF_FUNC_trace_printk;
> > >   static int (*get_smp_processor_id)(void) =
> > >       (void *)BPF_FUNC_get_smp_processor_id;
> > >   static int (*perf_event_output)(void *, struct bpf_map_def *, int, 
> > > void *, unsigned long) =
> > >       (void *)BPF_FUNC_perf_event_output;
> > >
> > >   struct bpf_map_def SEC("maps") channel = {
> > >       .type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
> > >       .key_size = sizeof(int),
> > >       .value_size = sizeof(u32),
> > >       .max_entries = __NR_CPUS__,
> > >   };
> > >
> > >   SEC("func_write=sys_write")
> > >   int func_write(void *ctx)
> > >   {
> > >       struct {
> > >           u64 ktime;
> > >           int cpuid;
> > >       } __attribute__((packed)) output_data;
> > >       char error_data[] = "Error: failed to output: %d\n";
> > >
> > >       output_data.cpuid = get_smp_processor_id();
> > >       output_data.ktime = ktime_get_ns();
> > >       int err = perf_event_output(ctx, &channel, 
> > > get_smp_processor_id(),
> > >                       &output_data, sizeof(output_data));
> > >       if (err)
> > >           trace_printk(error_data, sizeof(error_data), err);
> > >       return 0;
> > >   }
> > >   char _license[] SEC("license") = "GPL";
> > >   int _version SEC("version") = LINUX_VERSION_CODE;
> > >   /************************ END ***************************/
> > >
> > >   # ./perf record -a -e bpf-output/no-inherit,name=evt/ \
> > >                      -e ./test_bpf_output.c/map:channel.event=evt/ ls /
> > >   # ./perf script | grep ls
> > >            ls  2242 [003] 347851.557563: evt:  ffffffff811fd201 
> > > sys_write ...
> > >            ls  2242 [003] 347851.557571: evt:  ffffffff811fd201 
> > > sys_write ...
> > So, there is something strange here:
> >
> >          if (unlikely(event->oncpu != smp_processor_id()))
> >                  return -EOPNOTSUPP;

All failures have 'event->oncpu == -1' here. I guess we should suppress 
warning in
this case. But why event->oncpu becomes -1?

Thank you.