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7864d8f7c0
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.
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) ]
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: ae4f8ae16a ("libperf evlist: Allow mixing per-thread and per-cpu mmaps")
Reported-by: Tomáš Trnka <trnka@scm.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216441
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220905114209.8389-1-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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