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    Subject[PATCH 5.19 152/192] libperf evlist: Fix per-thread mmaps for multi-threaded targets
    Date
    From: Adrian Hunter <adrian.hunter@intel.com>

    [ Upstream commit 7864d8f7c088aad988c44c631f1ceed9179cf2cf ]

    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>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    tools/lib/perf/evlist.c | 50 +++++++++++++++++++++++++++++++++++++++++
    1 file changed, 50 insertions(+)

    diff --git a/tools/lib/perf/evlist.c b/tools/lib/perf/evlist.c
    index e6c98a6e3908e..6b1bafe267a42 100644
    --- 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);
    }

    --
    2.35.1


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