4 files changed, 16 insertions, 4 deletions

diff --git a/tools/perf/Documentation/perf-top.txt b/tools/perf/Documentation/perf-top.txt
index d864ea6fd367..4353262bc462 100644
--- a/tools/perf/Documentation/perf-top.txt
+++ b/tools/perf/Documentation/perf-top.txt
@@ -240,6 +240,9 @@ Default is to monitor all CPUS.
 --force::
         Don't do ownership validation.
 
+--num-thread-synthesize::
+        The number of threads to run when synthesizing events for existing processes.
+        By default, the number of threads equals to the number of online CPUs.
 
 INTERACTIVE PROMPTING KEYS
 --------------------------
diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index bc31b93cc1d8..477a8699f0b5 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -958,14 +958,16 @@ static int __cmd_top(struct perf_top *top)
         if (perf_session__register_idle_thread(top->session) < 0)
                 goto out_delete;
 
-        perf_set_multithreaded();
+        if (top->nr_threads_synthesize > 1)
+                perf_set_multithreaded();
 
         machine__synthesize_threads(&top->session->machines.host, &opts->target,
                                     top->evlist->threads, false,
                                     opts->proc_map_timeout,
-                                    (unsigned int)sysconf(_SC_NPROCESSORS_ONLN));
+                                    top->nr_threads_synthesize);
 
-        perf_set_singlethreaded();
+        if (top->nr_threads_synthesize > 1)
+                perf_set_singlethreaded();
 
         if (perf_hpp_list.socket) {
                 ret = perf_env__read_cpu_topology_map(&perf_env);
@@ -1118,6 +1120,7 @@ int cmd_top(int argc, const char **argv)
                 },
                 .max_stack           = sysctl_perf_event_max_stack,
                 .sym_pcnt_filter     = 5,
+                .nr_threads_synthesize = UINT_MAX,
         };
         struct record_opts *opts = &top.record_opts;
         struct target *target = &opts->target;
@@ -1227,6 +1230,8 @@ int cmd_top(int argc, const char **argv)
         OPT_BOOLEAN(0, "hierarchy", &symbol_conf.report_hierarchy,
                     "Show entries in a hierarchy"),
         OPT_BOOLEAN(0, "force", &symbol_conf.force, "don't complain, do it"),
+        OPT_UINTEGER(0, "num-thread-synthesize", &top.nr_threads_synthesize,
+                        "number of thread to run event synthesize"),
         OPT_END()
         };
         const char * const top_usage[] = {
diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index 0e678dd6bdbe..47eff4767edb 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -790,7 +790,10 @@ int perf_event__synthesize_threads(struct perf_tool *tool,
         if (n < 0)
                 return err;
 
-        thread_nr = nr_threads_synthesize;
+        if (nr_threads_synthesize == UINT_MAX)
+                thread_nr = sysconf(_SC_NPROCESSORS_ONLN);
+        else
+                thread_nr = nr_threads_synthesize;
 
         if (thread_nr <= 1) {
                 err = __perf_event__synthesize_threads(tool, process,
diff --git a/tools/perf/util/top.h b/tools/perf/util/top.h
index 9bdfb78a9a35..f4296e1e3bb8 100644
--- a/tools/perf/util/top.h
+++ b/tools/perf/util/top.h
@@ -37,6 +37,7 @@ struct perf_top {
         int                sym_pcnt_filter;
         const char         *sym_filter;
         float              min_percent;
+        unsigned int       nr_threads_synthesize;
 };
 
 #define CONSOLE_CLEAR ""