summaryrefslogtreecommitdiffstats
path: root/lib
diff options
context:
space:
mode:
authorJan Glauber <jglauber@cavium.com>2019-06-05 15:48:49 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2019-06-07 13:15:06 -0700
commit893a7d32e8e04ca4d6c882336b26ed660ca0a48d (patch)
treedc6946c02bd1d17178e8ac9b4925513834490e11 /lib
parentd93445225cd3c8eb0bf1350c04875576428b45b4 (diff)
lockref: Limit number of cmpxchg loop retries
The lockref cmpxchg loop is unbound as long as the spinlock is not taken. Depending on the hardware implementation of compare-and-swap a high number of loop retries might happen. Add an upper bound to the loop to force the fallback to spinlocks after some time. A retry value of 100 should not impact any hardware that does not have this issue. With the retry limit the performance of an open-close testcase improved between 60-70% on ThunderX2. Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Jan Glauber <jglauber@marvell.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib')
-rw-r--r--lib/lockref.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/lib/lockref.c b/lib/lockref.c
index 3d468b53d4c9..5b34bbd3eba8 100644
--- a/lib/lockref.c
+++ b/lib/lockref.c
@@ -9,6 +9,7 @@
* failure case.
*/
#define CMPXCHG_LOOP(CODE, SUCCESS) do { \
+ int retry = 100; \
struct lockref old; \
BUILD_BUG_ON(sizeof(old) != 8); \
old.lock_count = READ_ONCE(lockref->lock_count); \
@@ -21,6 +22,8 @@
if (likely(old.lock_count == prev.lock_count)) { \
SUCCESS; \
} \
+ if (!--retry) \
+ break; \
cpu_relax(); \
} \
} while (0)