Re: [PATCH]Perf top: Add ability to detect new threads dynamicallyduring 'perf top -p 'pid'' is running

From: David Ahern
Date: Tue Sep 04 2012 - 12:00:16 EST


On 8/22/12 8:37 AM, chenggang qin wrote:
> From: Chenggang Qin <chenggang.qin@xxxxxxxxx>
>
> While we use "perf top -p 'pid'" to monitor the symbols of specified
> processes, some new threads would be created by the monitored processes
> during "perf top" is running. In current version, these new threads and
> their symbols cannot be shown.
> This patch add ability to show these new threads.
>
> Signed-off-by: Chenggang Qin <chenggang.qcg@xxxxxxxxxx>
>
> ---
> tools/perf/builtin-top.c | 86 ++++++++++++++++++++++++++++++++++++++++++++--
> tools/perf/util/evlist.c | 2 ++
> 2 files changed, 85 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index 68cd61e..54c9cc1 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -882,7 +882,7 @@ static void perf_top__mmap_read(struct perf_top *top)
> perf_top__mmap_read_idx(top, i);
> }
>
> -static void perf_top__start_counters(struct perf_top *top)
> +static int perf_top__start_counters(struct perf_top *top)
> {
> struct perf_evsel *counter, *first;
> struct perf_evlist *evlist = top->evlist;
> @@ -929,6 +929,10 @@ try_again:
> group_fd) < 0) {
> int err = errno;
>
> + if (err == ESRCH) {
> + return err;
> + }
> +
> if (err == EPERM || err == EACCES) {
> ui__error_paranoid();
> goto out_err;
> @@ -994,7 +998,7 @@ try_again:
> goto out_err;
> }
>
> - return;
> + return 0;
>
> out_err:
> exit_browser(0);
> @@ -1018,6 +1022,77 @@ static int perf_top__setup_sample_type(struct perf_top *top)
> return 0;
> }
>
> +static int thread_map_cmp(struct thread_map *threads_a,
> + struct thread_map *threads_b)
> +{
> + int i, j;
> +
> + if (threads_a->nr != threads_b->nr) {
> + return 1;
> + } else {
> + for (i = 0; i < threads_b->nr; i++) {
> + for (j = 0; j < threads_a->nr; j++)
> + if (threads_b->map[i] == threads_a->map[j])
> + break;
> +
> + if (j == threads_a->nr)
> + return 1;
> + }
> +
> + return 0;
> + }
> +}
> +
> +static void check_new_threads(struct perf_top *top)
> +{
> + struct thread_map *new_thread_map;
> + struct perf_evsel *counter;
> + struct perf_evlist *evlist = top->evlist;
> +
> +retry:
> + new_thread_map = thread_map__new_str(top->target.pid, top->target.tid,
> + top->target.uid);
> + if (!new_thread_map)
> + return;
> +
> + if (thread_map_cmp(top->evlist->threads, new_thread_map) == 0) {
> + free(new_thread_map);
> + return;
> + } else {
> + list_for_each_entry(counter, &evlist->entries, node) {
> + perf_evsel__close(counter, top->evlist->cpus->nr,
> + top->evlist->threads->nr);
> + }
> +
> + if (top->evlist->mmap)
> + perf_evlist__munmap(top->evlist);
> +
> + if (top->evlist->pollfd) {
> + free(top->evlist->pollfd);
> + top->evlist->pollfd = NULL;
> + }
> +
> + top->evlist->nr_fds = 0;
> +
> + thread_map__delete(top->evlist->threads);
> + top->evlist->threads = new_thread_map;
> +
> + if (perf_top__start_counters(top) == ESRCH) {
> + while (thread_map_cmp(top->evlist->threads,
> + new_thread_map) == 0) {
> + new_thread_map = thread_map__new_str(top->target.pid,
> + top->target.tid,
> + top->target.uid);
> + if (!new_thread_map)
> + return;
> + }
> + goto retry;
> + }
> +
> + return;
> + }
> +}
> +

I think it would be better to respond to FORK (and EXIT) events and open
(close) counters accordingly. perf-top gets events when a thread is
created or terminated; it might as well use the events to react than to
poll every trip through the loop.

David
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