perf: builtin-record: Document and check that mmap_pages must be a power of two.

Now that we automatically point users at it, let's provide them some
guidance so that they hopefully don't just get mysterious EINVAL's
from the kernel.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1324301972-22740-4-git-send-email-nelhage@nelhage.com
Signed-off-by: Nelson Elhage <nelhage@nelhage.com>
[ committer note: Made it work after 50a682c ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 963d63dde457..fa1837088ca8 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -563,6 +563,8 @@ int perf_evlist__mmap(struct perf_evlist *evlist, unsigned int pages,
         /* 512 kiB: default amount of unprivileged mlocked memory */
         if (pages == UINT_MAX)
                 pages = (512 * 1024) / page_size;
+        else if (!is_power_of_2(pages))
+                return -EINVAL;
 
         mask = pages * page_size - 1;