From: Song Liu <songliubraving@fb.com>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: open list <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Namhyung Kim <namhyung@kernel.org>,
Mark Rutland <mark.rutland@arm.com>, Jiri Olsa <jolsa@redhat.com>,
"Kernel Team" <Kernel-team@fb.com>
Subject: Re: FIX Re: [PATCH v7 3/3] perf-stat: enable counting events for BPF programs
Date: Wed, 20 Jan 2021 16:40:46 +0000 [thread overview]
Message-ID: <498F663D-B3D5-4339-B076-B8D24FFD8B9A@fb.com> (raw)
In-Reply-To: <20210120163031.GU12699@kernel.org>
> On Jan 20, 2021, at 8:30 AM, Arnaldo Carvalho de Melo <acme@kernel.org> 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?
Song
[...]
next prev parent reply other threads:[~2021-01-20 16:46 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-29 21:42 [PATCH v7 0/3] Introduce perf-stat -b for BPF programs Song Liu
2020-12-29 21:42 ` [PATCH v7 1/3] bpftool: add Makefile target bootstrap Song Liu
2020-12-29 21:42 ` [PATCH v7 2/3] perf: support build BPF skeletons with perf Song Liu
2020-12-29 21:42 ` [PATCH v7 3/3] perf-stat: enable counting events for BPF programs Song Liu
2021-01-12 7:35 ` Namhyung Kim
2021-01-15 18:53 ` Arnaldo Carvalho de Melo
2021-01-18 19:38 ` Arnaldo Carvalho de Melo
2021-01-19 0:48 ` Song Liu
2021-01-19 14:31 ` Arnaldo Carvalho de Melo
2021-01-19 14:42 ` Arnaldo Carvalho de Melo
2021-01-19 16:31 ` Arnaldo Carvalho de Melo
2021-01-19 21:54 ` Song Liu
2021-01-19 22:30 ` Arnaldo Carvalho de Melo
2021-01-20 12:37 ` Arnaldo Carvalho de Melo
2021-01-20 13:01 ` Arnaldo Carvalho de Melo
2021-01-20 13:50 ` Arnaldo Carvalho de Melo
2021-01-20 16:30 ` FIX " Arnaldo Carvalho de Melo
2021-01-20 16:40 ` Song Liu [this message]
2021-01-20 17:04 ` Arnaldo Carvalho de Melo
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=498F663D-B3D5-4339-B076-B8D24FFD8B9A@fb.com \
--to=songliubraving@fb.com \
--cc=Kernel-team@fb.com \
--cc=acme@kernel.org \
--cc=alexander.shishkin@linux.intel.com \
--cc=jolsa@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=mingo@redhat.com \
--cc=namhyung@kernel.org \
--cc=peterz@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).