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| author | Jan Glauber <jglauber@cavium.com> | 2019-06-05 15:48:49 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-06-07 13:15:06 -0700 |
| commit | 893a7d32e8e04ca4d6c882336b26ed660ca0a48d (patch) | |
| tree | dc6946c02bd1d17178e8ac9b4925513834490e11 | |
| parent | d93445225cd3c8eb0bf1350c04875576428b45b4 (diff) | |
| download | lwn-893a7d32e8e04ca4d6c882336b26ed660ca0a48d.tar.gz lwn-893a7d32e8e04ca4d6c882336b26ed660ca0a48d.zip | |
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>
| -rw-r--r-- | lib/lockref.c | 3 |
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) |