linux/tools/lib
Adrian Hunter 7864d8f7c0 libperf evlist: Fix per-thread mmaps for multi-threaded targets
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>
2022-09-08 12:17:22 -03:00
..
api Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
bpf bpf: Disallow bpf programs call prog_run command. 2022-08-10 09:43:07 -07:00
perf libperf evlist: Fix per-thread mmaps for multi-threaded targets 2022-09-08 12:17:22 -03:00
subcmd libsubcmd: Fix OPTION_GROUP sorting 2022-04-22 12:32:01 +02:00
symbol libsymbols kallsyms: Move hex2u64 out of header 2020-05-05 16:35:32 -03:00
thermal tools/lib/thermal: remove unneeded semicolon 2022-05-19 12:11:52 +02:00
traceevent libtraceevent: Add __rel_loc relative location attribute support 2021-12-06 15:37:22 -05:00
argv_split.c
bitmap.c Bitmap patches for v6.0-rc1 2022-08-07 17:52:35 -07:00
ctype.c
find_bit.c tools: sync tools/bitmap with mother linux 2022-01-15 08:47:31 -08:00
hweight.c
list_sort.c tools lib: Adopt list_sort() from the kernel sources 2021-10-20 10:30:59 -03:00
rbtree.c tools/: replace HTTP links with HTTPS ones 2020-08-07 11:33:21 -07:00
slab.c tools: Move gfp.h and slab.h from radix-tree to lib 2022-02-20 08:44:37 +02:00
str_error_r.c
string.c tools lib: Adopt memchr_inv() from kernel 2020-11-27 08:34:52 -03:00
vsprintf.c
zalloc.c