perf evlist: Expose perf_event_mlock_kb_in_pages() helper

When the user doesn't set --mmap-pages, perf_evlist__mmap() will do it
by reading the maximum possible for a non-root user from the
/proc/sys/kernel/perf_event_mlock_kb file.

Expose that function so that 'perf trace' can, for root users, to bump
mmap-pages to a higher value for root, based on the contents of this
proc file.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-xay69plylwibpb3l4isrpl1k@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 27 insertions, 17 deletions

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 4c9f510ae18d..6fb5725821de 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -986,26 +986,34 @@ out_unmap:
         return -1;
 }
 
-static size_t perf_evlist__mmap_size(unsigned long pages)
+unsigned long perf_event_mlock_kb_in_pages(void)
 {
-        if (pages == UINT_MAX) {
-                int max;
+        unsigned long pages;
+        int max;
 
-                if (sysctl__read_int("kernel/perf_event_mlock_kb", &max) < 0) {
-                        /*
-                         * Pick a once upon a time good value, i.e. things look
-                         * strange since we can't read a sysctl value, but lets not
-                         * die yet...
-                         */
-                        max = 512;
-                } else {
-                        max -= (page_size / 1024);
-                }
+        if (sysctl__read_int("kernel/perf_event_mlock_kb", &max) < 0) {
+                /*
+                 * Pick a once upon a time good value, i.e. things look
+                 * strange since we can't read a sysctl value, but lets not
+                 * die yet...
+                 */
+                max = 512;
+        } else {
+                max -= (page_size / 1024);
+        }
+
+        pages = (max * 1024) / page_size;
+        if (!is_power_of_2(pages))
+                pages = rounddown_pow_of_two(pages);
 
-                pages = (max * 1024) / page_size;
-                if (!is_power_of_2(pages))
-                        pages = rounddown_pow_of_two(pages);
-        } else if (!is_power_of_2(pages))
+        return pages;
+}
+
+static size_t perf_evlist__mmap_size(unsigned long pages)
+{
+        if (pages == UINT_MAX)
+                pages = perf_event_mlock_kb_in_pages();
+        else if (!is_power_of_2(pages))
                 return 0;
 
         return (pages + 1) * page_size;
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index da46423998e8..208897a646ca 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -158,6 +158,8 @@ int perf_evlist__parse_mmap_pages(const struct option *opt,
                                   const char *str,
                                   int unset);
 
+unsigned long perf_event_mlock_kb_in_pages(void);
+
 int perf_evlist__mmap_ex(struct perf_evlist *evlist, unsigned int pages,
                          bool overwrite, unsigned int auxtrace_pages,
                          bool auxtrace_overwrite);