The --num-thread option is to set number of reader thread.  Default
value is 0 which will be converted to 1/4 of number of mmaps.

Signed-off-by: Namhyung Kim <namhy...@kernel.org>
---
 tools/perf/builtin-top.c | 49 +++++++++++++++++++++++++++++++++++-------------
 tools/perf/util/top.h    |  1 +
 2 files changed, 37 insertions(+), 13 deletions(-)

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index f3ab46b234b6..fc9715b046b3 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -838,10 +838,10 @@ struct collector_arg {
 
 static void collect_hists(struct perf_top *top, struct hists *hists)
 {
-       int i, k;
+       unsigned int i, k;
        struct perf_evsel *evsel;
 
-       for (i = 0, k = 0; i < top->evlist->nr_mmaps; i++) {
+       for (i = 0, k = 0; i < top->nr_threads; i++) {
                evlist__for_each(top->evlist, evsel) {
                        struct hists *src_hists = &hists[k++];
                        struct hists *dst_hists = evsel__hists(evsel);
@@ -900,6 +900,7 @@ static int hist_iter__top_callback(struct hist_entry_iter 
*iter,
 
 struct reader_arg {
        int                     idx;
+       int                     nr_idx;
        struct perf_top         *top;
        struct hists            *hists;
        struct perf_top_stats   stats;
@@ -993,7 +994,7 @@ static void perf_event__process_sample(struct reader_arg 
*rarg,
        addr_location__put(&al);
 }
 
-static void perf_top__mmap_read(struct reader_arg *rarg)
+static void perf_top__mmap_read_idx(struct reader_arg *rarg, int idx)
 {
        struct perf_sample sample;
        struct perf_evsel *evsel;
@@ -1001,7 +1002,6 @@ static void perf_top__mmap_read(struct reader_arg *rarg)
        struct perf_session *session = top->session;
        union perf_event *event;
        struct machine *machine;
-       int idx = rarg->idx;
        u8 origin;
        int ret;
 
@@ -1067,6 +1067,14 @@ static void perf_top__mmap_read(struct reader_arg *rarg)
        }
 }
 
+static void perf_top__mmap_read(struct reader_arg *rarg)
+{
+       int i;
+
+       for (i = 0; i < rarg->nr_idx; i++)
+               perf_top__mmap_read_idx(rarg, rarg->idx + i);
+}
+
 static void *mmap_read_worker(void *arg)
 {
        struct reader_arg *rarg = arg;
@@ -1160,7 +1168,8 @@ static int __cmd_top(struct perf_top *top)
        struct reader_arg *rargs = NULL;
        struct collector_arg carg;
        int ret;
-       int i;
+       unsigned int i;
+       int idx, nr_idx, rem;
 
        top->session = perf_session__new(NULL, false, NULL);
        if (top->session == NULL)
@@ -1211,34 +1220,47 @@ static int __cmd_top(struct perf_top *top)
        /* Wait for a minimal set of events before starting the snapshot */
        perf_evlist__poll(top->evlist, 100);
 
+       if (top->nr_threads == 0)
+               top->nr_threads = top->evlist->nr_mmaps / 4 ?: 1;
+       if ((int)top->nr_threads > top->evlist->nr_mmaps)
+               top->nr_threads = top->evlist->nr_mmaps;
+
+       nr_idx = top->evlist->nr_mmaps / top->nr_threads;
+       rem = top->evlist->nr_mmaps % top->nr_threads;
+
        ret = -1;
-       readers = calloc(sizeof(pthread_t), top->evlist->nr_mmaps);
+       readers = calloc(sizeof(pthread_t), top->nr_threads);
        if (readers == NULL)
                goto out_delete;
 
-       rargs = calloc(sizeof(*rargs), top->evlist->nr_mmaps);
+       rargs = calloc(sizeof(*rargs), top->nr_threads);
        if (rargs == NULL)
                goto out_free;
 
-       hists = calloc(sizeof(*hists), top->evlist->nr_mmaps * 
top->evlist->nr_entries);
+       hists = calloc(sizeof(*hists), top->nr_threads * 
top->evlist->nr_entries);
        if (hists == NULL)
                goto out_free;
 
-       for (i = 0; i < top->evlist->nr_mmaps * top->evlist->nr_entries; i++)
+       for (i = 0; i < top->nr_threads * top->evlist->nr_entries; i++)
                __hists__init(&hists[i]);
 
-       for (i = 0; i < top->evlist->nr_mmaps; i++) {
+       for (i = 0, idx = 0; i < top->nr_threads; i++) {
                struct reader_arg *rarg = &rargs[i];
 
-               rarg->idx = i;
                rarg->top = top;
                rarg->hists = &hists[i * top->evlist->nr_entries];
 
+               rarg->idx = idx;
+               rarg->nr_idx = nr_idx;
+               if (rem-- > 0)
+                       rarg->nr_idx++;
+               idx += rarg->nr_idx;
+
                perf_top__mmap_read(rarg);
        }
        collect_hists(top, hists);
 
-       for (i = 0; i < top->evlist->nr_mmaps; i++) {
+       for (i = 0; i < top->nr_threads; i++) {
                if (pthread_create(&readers[i], NULL, mmap_read_worker, 
&rargs[i]))
                        goto out_join;
        }
@@ -1259,7 +1281,7 @@ static int __cmd_top(struct perf_top *top)
 out_join:
        pthread_join(ui_thread, NULL);
        pthread_join(collector, NULL);
-       for (i = 0; i < top->evlist->nr_mmaps; i++) {
+       for (i = 0; i < top->nr_threads; i++) {
                pthread_join(readers[i], NULL);
        }
 
@@ -1458,6 +1480,7 @@ int cmd_top(int argc, const char **argv, const char 
*prefix __maybe_unused)
        OPT_CALLBACK('j', "branch-filter", &opts->branch_stack,
                     "branch filter mask", "branch stack filter modes",
                     parse_branch_stack),
+       OPT_UINTEGER(0, "num-thread", &top.nr_threads, "number of thread to 
run"),
        OPT_END()
        };
        const char * const top_usage[] = {
diff --git a/tools/perf/util/top.h b/tools/perf/util/top.h
index 55eb5aebae59..916ba36b0ac0 100644
--- a/tools/perf/util/top.h
+++ b/tools/perf/util/top.h
@@ -43,6 +43,7 @@ struct perf_top {
        int                sym_pcnt_filter;
        const char         *sym_filter;
        float              min_percent;
+       unsigned int       nr_threads;
 };
 
 #define CONSOLE_CLEAR ""
-- 
2.6.2

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