From: Jan Glauber <jglauber@cavium.com>
To: linux-kernel@vger.kernel.org
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
linux-arm-kernel@lists.infradead.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Jayachandran Chandrasekharan Nair <jnair@marvell.com>,
Jan Glauber <jglauber@marvell.com>
Subject: [PATCH] lockref: Limit number of cmpxchg loop retries
Date: Wed, 5 Jun 2019 15:48:49 +0200 [thread overview]
Message-ID: <20190605134849.28108-1-jglauber@marvell.com> (raw)
In-Reply-To: <CAHk-=wjPqcPYkiWKFc=R3+18DXqEhV+Nfbo=JWa32Xp8Nze67g@mail.gmail.com>
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>
---
lib/lockref.c | 3 +++
1 file changed, 3 insertions(+)
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)
--
2.21.0
next prev parent reply other threads:[~2019-06-05 13:49 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-29 14:52 [RFC] Disable lockref on arm64 Jan Glauber
2019-05-01 16:01 ` Will Deacon
2019-05-02 8:38 ` Jan Glauber
2019-05-01 16:41 ` Linus Torvalds
2019-05-02 8:27 ` Jan Glauber
2019-05-02 16:12 ` Linus Torvalds
2019-05-02 23:19 ` Jayachandran Chandrasekharan Nair
2019-05-03 19:40 ` Linus Torvalds
2019-05-06 6:13 ` [EXT] " Jayachandran Chandrasekharan Nair
2019-05-06 17:13 ` Linus Torvalds
2019-05-06 18:10 ` Will Deacon
2019-05-18 4:24 ` Jayachandran Chandrasekharan Nair
2019-05-18 10:00 ` Ard Biesheuvel
2019-05-22 16:04 ` Will Deacon
2019-06-12 4:10 ` Jayachandran Chandrasekharan Nair
2019-06-12 9:31 ` Will Deacon
2019-06-14 7:09 ` Jayachandran Chandrasekharan Nair
2019-06-14 9:58 ` Will Deacon
2019-06-14 10:24 ` Ard Biesheuvel
2019-06-14 10:38 ` Will Deacon
2019-06-15 4:21 ` Kees Cook
2019-06-15 8:47 ` Ard Biesheuvel
2019-06-15 13:59 ` Kees Cook
2019-06-15 14:18 ` Ard Biesheuvel
2019-06-16 21:31 ` Kees Cook
2019-06-17 11:33 ` Ard Biesheuvel
2019-06-17 17:26 ` Will Deacon
2019-06-17 20:07 ` Jayachandran Chandrasekharan Nair
2019-06-18 5:41 ` Kees Cook
2019-06-13 9:53 ` Hanjun Guo
2019-06-05 13:48 ` Jan Glauber [this message]
2019-06-05 20:16 ` [PATCH] lockref: Limit number of cmpxchg loop retries Linus Torvalds
2019-06-06 8:03 ` Jan Glauber
2019-06-06 9:41 ` Will Deacon
2019-06-06 10:28 ` Jan Glauber
2019-06-07 7:27 ` Jan Glauber
2019-06-07 20:14 ` Linus Torvalds
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