lib/find_bit_benchmark.c: avoid soft lockup in test_find_first_bit()

BugLink: http://bugs.launchpad.net/bugs/1794889
[ Upstream commit 4ba281d5bd9907355e6b79fb72049c9ed50cc670 ]

test_find_first_bit() is intentionally sub-optimal, and may cause soft
lockup due to long time of run on some systems.  So decrease length of
bitmap to traverse to avoid lockup.

With the change below, time of test execution doesn't exceed 0.2 seconds
on my testing system.

Link: http://lkml.kernel.org/r/20180420171949.15710-1-ynorov@caviumnetworks.com
Fixes: 4441fca0a27f5 ("lib: test module for find_*_bit() functions")
Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/lib/test_find_bit.c b/lib/test_find_bit.c
index f4394a36f9aa2b60a05624308a60ba59897f1606..44ceda470a2ac3afeaac42afea6ae3df48eb7f1d 100644 (file)
--- a/lib/test_find_bit.c
+++ b/lib/test_find_bit.c
@@ -118,7 +118,12 @@ static int __init find_bit_test(void)
        test_find_next_bit(bitmap, BITMAP_LEN);
        test_find_next_zero_bit(bitmap, BITMAP_LEN);
        test_find_last_bit(bitmap, BITMAP_LEN);
-       test_find_first_bit(bitmap, BITMAP_LEN);
+
+       /*
+        * test_find_first_bit() may take some time, so
+        * traverse only part of bitmap to avoid soft lockup.
+        */
+       test_find_first_bit(bitmap, BITMAP_LEN / 10);
 
        pr_err("\nStart testing find_bit() with sparse bitmap\n");