Messages in this thread | | | From | Namhyung Kim <> | Date | Tue, 6 Sep 2022 10:50:31 -0700 | Subject | Re: [PATCH V2] libperf evlist: Fix per-thread mmaps for multi-threaded targets |
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On Mon, Sep 5, 2022 at 4:42 AM Adrian Hunter <adrian.hunter@intel.com> wrote: > > The offending commit removed mmap_per_thread(), which did not consider > the different set-output rules for per-thread mmaps i.e. in the per-thread > case set-output is used for file descriptors of the same thread not the > same cpu. > > This was not immediately noticed because it only happens with > multi-threaded targets and we do not have a test for that yet.
Yeah, this is unfortunate. I feel like I need to spend some time on it.
> > Reinstate mmap_per_thread() expanding it to cover also system-wide per-cpu > events i.e. to continue to allow the mixing of per-thread and per-cpu > mmaps. > > Debug messages (with -vv) show the file descriptors that are opened with > sys_perf_event_open. New debug messages are added (needs -vvv) that show > also which file descriptors are mmapped and which are redirected with > set-output. > > In the per-cpu case (cpu != -1) file descriptors for the same CPU are > set-output to the first file descriptor for that CPU. > > In the per-thread case (cpu == -1) file descriptors for the same thread are > set-output to the first file descriptor for that thread. > > Example (process 17489 has 2 threads): > > Before (but with new debug prints): > > $ perf record --no-bpf-event -vvv --per-thread -p 17489 > <SNIP> > sys_perf_event_open: pid 17489 cpu -1 group_fd -1 flags 0x8 = 5 > sys_perf_event_open: pid 17490 cpu -1 group_fd -1 flags 0x8 = 6 > <SNIP> > libperf: idx 0: mmapping fd 5 > libperf: idx 0: set output fd 6 -> 5 > failed to mmap with 22 (Invalid argument) > > After: > > $ perf record --no-bpf-event -vvv --per-thread -p 17489 > <SNIP> > sys_perf_event_open: pid 17489 cpu -1 group_fd -1 flags 0x8 = 5 > sys_perf_event_open: pid 17490 cpu -1 group_fd -1 flags 0x8 = 6 > <SNIP> > libperf: mmap_per_thread: nr cpu values (may include -1) 1 nr threads 2 > libperf: idx 0: mmapping fd 5 > libperf: idx 1: mmapping fd 6 > <SNIP> > [ perf record: Woken up 2 times to write data ] > [ perf record: Captured and wrote 0.018 MB perf.data (15 samples) ]
It'd be nice if the example had 2 events so that it could check the set-output rule actually worked.
Thanks, Namhyung
> > Per-cpu example (process 20341 has 2 threads, same as above): > > $ perf record --no-bpf-event -vvv -p 20341 > <SNIP> > sys_perf_event_open: pid 20341 cpu 0 group_fd -1 flags 0x8 = 5 > sys_perf_event_open: pid 20342 cpu 0 group_fd -1 flags 0x8 = 6 > sys_perf_event_open: pid 20341 cpu 1 group_fd -1 flags 0x8 = 7 > sys_perf_event_open: pid 20342 cpu 1 group_fd -1 flags 0x8 = 8 > sys_perf_event_open: pid 20341 cpu 2 group_fd -1 flags 0x8 = 9 > sys_perf_event_open: pid 20342 cpu 2 group_fd -1 flags 0x8 = 10 > sys_perf_event_open: pid 20341 cpu 3 group_fd -1 flags 0x8 = 11 > sys_perf_event_open: pid 20342 cpu 3 group_fd -1 flags 0x8 = 12 > sys_perf_event_open: pid 20341 cpu 4 group_fd -1 flags 0x8 = 13 > sys_perf_event_open: pid 20342 cpu 4 group_fd -1 flags 0x8 = 14 > sys_perf_event_open: pid 20341 cpu 5 group_fd -1 flags 0x8 = 15 > sys_perf_event_open: pid 20342 cpu 5 group_fd -1 flags 0x8 = 16 > sys_perf_event_open: pid 20341 cpu 6 group_fd -1 flags 0x8 = 17 > sys_perf_event_open: pid 20342 cpu 6 group_fd -1 flags 0x8 = 18 > sys_perf_event_open: pid 20341 cpu 7 group_fd -1 flags 0x8 = 19 > sys_perf_event_open: pid 20342 cpu 7 group_fd -1 flags 0x8 = 20 > <SNIP> > libperf: mmap_per_cpu: nr cpu values 8 nr threads 2 > libperf: idx 0: mmapping fd 5 > libperf: idx 0: set output fd 6 -> 5 > libperf: idx 1: mmapping fd 7 > libperf: idx 1: set output fd 8 -> 7 > libperf: idx 2: mmapping fd 9 > libperf: idx 2: set output fd 10 -> 9 > libperf: idx 3: mmapping fd 11 > libperf: idx 3: set output fd 12 -> 11 > libperf: idx 4: mmapping fd 13 > libperf: idx 4: set output fd 14 -> 13 > libperf: idx 5: mmapping fd 15 > libperf: idx 5: set output fd 16 -> 15 > libperf: idx 6: mmapping fd 17 > libperf: idx 6: set output fd 18 -> 17 > libperf: idx 7: mmapping fd 19 > libperf: idx 7: set output fd 20 -> 19 > <SNIP> > [ perf record: Woken up 7 times to write data ] > [ perf record: Captured and wrote 0.020 MB perf.data (17 samples) ] > > Fixes: ae4f8ae16a07 ("libperf evlist: Allow mixing per-thread and per-cpu mmaps") > Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
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