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: ae4f8ae16a078964 ("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>

diff --git a/tools/lib/perf/evlist.c b/tools/lib/perf/evlist.c
index e6c98a6e3908e20f8c68946f677b7161540f0e47..6b1bafe267a4219befee9d9c0dffbcd77fd70a22 100644 (file)
--- a/tools/lib/perf/evlist.c
+++ b/tools/lib/perf/evlist.c
@@ -486,6 +486,7 @@ mmap_per_evsel(struct perf_evlist *evlist, struct perf_evlist_mmap_ops *ops,
                        if (ops->idx)
                                ops->idx(evlist, evsel, mp, idx);
 
+                       pr_debug("idx %d: mmapping fd %d\n", idx, *output);
                        if (ops->mmap(map, mp, *output, evlist_cpu) < 0)
                                return -1;
 
@@ -494,6 +495,7 @@ mmap_per_evsel(struct perf_evlist *evlist, struct perf_evlist_mmap_ops *ops,
                        if (!idx)
                                perf_evlist__set_mmap_first(evlist, map, overwrite);
                } else {
+                       pr_debug("idx %d: set output fd %d -> %d\n", idx, fd, *output);
                        if (ioctl(fd, PERF_EVENT_IOC_SET_OUTPUT, *output) != 0)
                                return -1;
 
@@ -519,6 +521,48 @@ mmap_per_evsel(struct perf_evlist *evlist, struct perf_evlist_mmap_ops *ops,
        return 0;
 }
 
+static int
+mmap_per_thread(struct perf_evlist *evlist, struct perf_evlist_mmap_ops *ops,
+               struct perf_mmap_param *mp)
+{
+       int nr_threads = perf_thread_map__nr(evlist->threads);
+       int nr_cpus    = perf_cpu_map__nr(evlist->all_cpus);
+       int cpu, thread, idx = 0;
+       int nr_mmaps = 0;
+
+       pr_debug("%s: nr cpu values (may include -1) %d nr threads %d\n",
+                __func__, nr_cpus, nr_threads);
+
+       /* per-thread mmaps */
+       for (thread = 0; thread < nr_threads; thread++, idx++) {
+               int output = -1;
+               int output_overwrite = -1;
+
+               if (mmap_per_evsel(evlist, ops, idx, mp, 0, thread, &output,
+                                  &output_overwrite, &nr_mmaps))
+                       goto out_unmap;
+       }
+
+       /* system-wide mmaps i.e. per-cpu */
+       for (cpu = 1; cpu < nr_cpus; cpu++, idx++) {
+               int output = -1;
+               int output_overwrite = -1;
+
+               if (mmap_per_evsel(evlist, ops, idx, mp, cpu, 0, &output,
+                                  &output_overwrite, &nr_mmaps))
+                       goto out_unmap;
+       }
+
+       if (nr_mmaps != evlist->nr_mmaps)
+               pr_err("Miscounted nr_mmaps %d vs %d\n", nr_mmaps, evlist->nr_mmaps);
+
+       return 0;
+
+out_unmap:
+       perf_evlist__munmap(evlist);
+       return -1;
+}
+
 static int
 mmap_per_cpu(struct perf_evlist *evlist, struct perf_evlist_mmap_ops *ops,
             struct perf_mmap_param *mp)
@@ -528,6 +572,8 @@ mmap_per_cpu(struct perf_evlist *evlist, struct perf_evlist_mmap_ops *ops,
        int nr_mmaps = 0;
        int cpu, thread;
 
+       pr_debug("%s: nr cpu values %d nr threads %d\n", __func__, nr_cpus, nr_threads);
+
        for (cpu = 0; cpu < nr_cpus; cpu++) {
                int output = -1;
                int output_overwrite = -1;
@@ -569,6 +615,7 @@ int perf_evlist__mmap_ops(struct perf_evlist *evlist,
                          struct perf_evlist_mmap_ops *ops,
                          struct perf_mmap_param *mp)
 {
+       const struct perf_cpu_map *cpus = evlist->all_cpus;
        struct perf_evsel *evsel;
 
        if (!ops || !ops->get || !ops->mmap)
@@ -588,6 +635,9 @@ int perf_evlist__mmap_ops(struct perf_evlist *evlist,
        if (evlist->pollfd.entries == NULL && perf_evlist__alloc_pollfd(evlist) < 0)
                return -ENOMEM;
 
+       if (perf_cpu_map__empty(cpus))
+               return mmap_per_thread(evlist, ops, mp);
+
        return mmap_per_cpu(evlist, ops, mp);
 }