2023-01-17 12:49 UTC+0800 ~ tong@xxxxxxxxxxxxx
> From: Tonghao Zhang <tong@xxxxxxxxxxxxx>
>
> The number of online cpu may be not equal to possible cpu.
> bpftool prog profile, can not create pmu event on possible
> but not online cpu.
s/not/on/ ?
>
> $ dmidecode -s system-product-name
> PowerEdge R620
> $ cat /sys/devices/system/cpu/online
> 0-31
> $ cat /sys/devices/system/cpu/possible
> 0-47
>
> To fix this issue, use online cpu instead of possible, to
> create perf event and other resource.
>
> Signed-off-by: Tonghao Zhang <tong@xxxxxxxxxxxxx>
> Cc: Quentin Monnet <quentin@xxxxxxxxxxxxx>
> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
> Cc: Martin KaFai Lau <martin.lau@xxxxxxxxx>
> Cc: Song Liu <song@xxxxxxxxxx>
> Cc: Yonghong Song <yhs@xxxxxx>
> Cc: John Fastabend <john.fastabend@xxxxxxxxx>
> Cc: KP Singh <kpsingh@xxxxxxxxxx>
> Cc: Stanislav Fomichev <sdf@xxxxxxxxxx>
> Cc: Hao Luo <haoluo@xxxxxxxxxx>
> Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> tools/bpf/bpftool/prog.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
> index cfc9fdc1e863..08b352dd799e 100644
> --- a/tools/bpf/bpftool/prog.c
> +++ b/tools/bpf/bpftool/prog.c
> @@ -2056,6 +2056,7 @@ static int profile_parse_metrics(int argc, char **argv)
>
> static void profile_read_values(struct profiler_bpf *obj)
> {
> + __u32 possible_cpus = libbpf_num_possible_cpus();
> __u32 m, cpu, num_cpu = obj->rodata->num_cpu;
> int reading_map_fd, count_map_fd;
> __u64 counts[num_cpu];
> @@ -2080,7 +2081,7 @@ static void profile_read_values(struct profiler_bpf *obj)
> profile_total_count += counts[cpu];
>
> for (m = 0; m < ARRAY_SIZE(metrics); m++) {
> - struct bpf_perf_event_value values[num_cpu];
> + struct bpf_perf_event_value values[possible_cpus];
>
> if (!metrics[m].selected)
> continue;
> @@ -2321,7 +2322,7 @@ static int do_profile(int argc, char **argv)
> if (num_metric <= 0)
> goto out;
>
> - num_cpu = libbpf_num_possible_cpus();
> + num_cpu = libbpf_num_online_cpus();
> if (num_cpu <= 0) {
> p_err("failed to identify number of CPUs");
> goto out;
Thanks, but it doesn't seem to be enough to solve the issue. How did you
test it? With your series applied locally, I'm trying the following
(Intel x86_64, CPUs: 0..7):
# echo 0 > /sys/devices/system/cpu/cpu2/online
# ./bpftool prog profile id 1525 duration 1 cycles instructions
Error: failed to create event cycles on cpu 2
It seems that we're still trying to open the perf events on the offline
CPU in profile_open_perf_events(), because even though we try to use
fewer of the possible CPUs we're still referencing them in order by
their index. So it works if I only disabled the last CPUs instead (#7,
then #6, ...), but to work with _any_ CPU disabled, we would need to
retrieve the list of online CPUs.
