Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old
in __get_reqs_available. 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@xxxxxxxxx>
Cc: Benjamin LaHaise <bcrl@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
---
fs/aio.c | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)
diff --git a/fs/aio.c b/fs/aio.c
index 3c249b938632..054897f59c5e 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -951,16 +951,13 @@ static bool __get_reqs_available(struct kioctx *ctx)
local_irq_save(flags);
kcpu = this_cpu_ptr(ctx->cpu);
if (!kcpu->reqs_available) {
- int old, avail = atomic_read(&ctx->reqs_available);
+ int avail = atomic_read(&ctx->reqs_available);
do {
if (avail < ctx->req_batch)
goto out;
-
- old = avail;
- avail = atomic_cmpxchg(&ctx->reqs_available,
- avail, avail - ctx->req_batch);
- } while (avail != old);
+ } while (!atomic_try_cmpxchg(&ctx->reqs_available,
+ &avail, avail - ctx->req_batch));
kcpu->reqs_available += ctx->req_batch;
}
--
2.35.3
