lkml.org 
[lkml]   [2022]   [Jul]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v2] block/rq_qos: Use atomic_try_cmpxchg in atomic_inc_below
Date
Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old in
atomic_inc_below. x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after cmpxchg (and related move instruction
in front of cmpxchg).

Also, atomic_try_cmpxchg implicitly assigns old *ptr value to "old" when
cmpxchg fails, enabling further code simplifications.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
---
v2: Split patch from the original big patch
---
block/blk-rq-qos.c | 10 ++--------
1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c
index d3a75693adbf..88f0fe7dcf54 100644
--- a/block/blk-rq-qos.c
+++ b/block/blk-rq-qos.c
@@ -10,16 +10,10 @@ static bool atomic_inc_below(atomic_t *v, unsigned int below)
{
unsigned int cur = atomic_read(v);

- for (;;) {
- unsigned int old;
-
+ do {
if (cur >= below)
return false;
- old = atomic_cmpxchg(v, cur, cur + 1);
- if (old == cur)
- break;
- cur = old;
- }
+ } while (!atomic_try_cmpxchg(v, &cur, cur + 1));

return true;
}
--
2.35.3
\
 
 \ /
  Last update: 2022-07-12 17:14    [W:0.071 / U:0.072 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site