tree dc6946c02bd1d17178e8ac9b4925513834490e11
parent d93445225cd3c8eb0bf1350c04875576428b45b4
author Jan Glauber <jglauber@cavium.com> 1559742529 +0200
committer Linus Torvalds <torvalds@linux-foundation.org> 1559938506 -0700

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>