Em Wed, Jan 20, 2021 at 04:40:46PM +0000, Song Liu escreveu: > > > > On Jan 20, 2021, at 8:30 AM, Arnaldo Carvalho de Melo <[email protected]> > > wrote: > > > > Em Wed, Jan 20, 2021 at 10:50:13AM -0300, Arnaldo Carvalho de Melo escreveu: > >> So sizeof(struct bpf_perf_event_value) == 24 and it is a per-cpu array, the > >> machine has 24 cpus, why is the kernel thinking it has more and end up > >> zeroing > >> entries after the 24 cores? Some percpu map subtlety (or obvious thing > >> ;-\) I'm > >> missing? > >> > >> Checking lookups into per cpu maps in sample code now... > > > > (gdb) run stat -b 244 -I 1000 -e cycles > > Starting program: /root/bin/perf stat -b 244 -I 1000 -e cycles > > [Thread debugging using libthread_db enabled] > > Using host libthread_db library "/lib64/libthread_db.so.1". > > libbpf: elf: skipping unrecognized data section(9) .eh_frame > > libbpf: elf: skipping relo section(15) .rel.eh_frame for section(9) > > .eh_frame > > > > Breakpoint 1, bpf_program_profiler__read (evsel=0xce02c0) at > > util/bpf_counter.c:217 > > 217 if (list_empty(&evsel->bpf_counter_list)) > > (gdb) p num_ > > num_cpu num_groups num_leaps num_print_iv > > num_stmts num_transitions num_warnings_issued > > num_cpu_bpf num_ifs num_print_interval num_srcfiles > > num_to_str num_types > > (gdb) p num_cpu > > $1 = 24 > > (gdb) p num_cpu_bpf > > $2 = 32 > > (gdb) > > > > Humm, why? > > > > But then libbpf and the sample/bpf/ code use it this way: > > > > > > diff --git a/tools/perf/util/bpf_counter.c b/tools/perf/util/bpf_counter.c > > index 8c977f038f497fc1..7dd3d57aba4f620c 100644 > > --- a/tools/perf/util/bpf_counter.c > > +++ b/tools/perf/util/bpf_counter.c > > @@ -207,7 +207,8 @@ static int bpf_program_profiler__enable(struct evsel > > *evsel) > > static int bpf_program_profiler__read(struct evsel *evsel) > > { > > int num_cpu = evsel__nr_cpus(evsel); > > - struct bpf_perf_event_value values[num_cpu]; > > + int num_cpu_bpf = libbpf_num_possible_cpus(); > > + struct bpf_perf_event_value values[num_cpu > num_cpu_bpf ? num_cpu : > > num_cpu_bpf]; > > struct bpf_counter *counter; > > int reading_map_fd; > > __u32 key = 0; > > > > ------------------------------------------------------------- > > > > [root@five ~]# cat /sys/devices/system/cpu/possible > > 0-31 > > [root@five ~]# > > > > I bet that in your test systems evsel__nr_cpus(evsel) matches > > /sys/devices/system/cpu/possible and thus you don't see the problem. > > Thanks Arnaldo! > > Yes, my system have same online and possible CPUs. > > Since possible_cpu >= online_cpu, maybe we can use num_cpu_bpf in > bpf_program_profiler__read() without he extra check?
That is what I'll do, no need to resubmit, I'll audit the other bits to see if something else needs changing. - Arnaldo
