The patch titled
Subject: aio: use atomic_try_cmpxchg in __get_reqs_available
has been added to the -mm mm-nonmm-unstable branch. Its filename is
aio-use-atomic_try_cmpxchg-in-__get_reqs_available.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/aio-use-atomic_try_cmpxchg-in-__get_reqs_available.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Uros Bizjak <ubizjak@xxxxxxxxx>
Subject: aio: use atomic_try_cmpxchg in __get_reqs_available
Date: Thu, 14 Jul 2022 18:48:51 +0200
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.
Link: https://lkml.kernel.org/r/20220714164851.3055-1-ubizjak@xxxxxxxxx
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Cc: Benjamin LaHaise <bcrl@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/aio.c | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)
--- a/fs/aio.c~aio-use-atomic_try_cmpxchg-in-__get_reqs_available
+++ a/fs/aio.c
@@ -951,16 +951,13 @@ static bool __get_reqs_available(struct
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;
}
_
Patches currently in -mm which might be from ubizjak@xxxxxxxxx are
llist-use-try_cmpxchg-in-llist_add_batch-and-llist_del_first.patch
epoll-use-try_cmpxchg-in-list_add_tail_lockless.patch
buffer-use-try_cmpxchg-in-discard_buffer.patch
aio-use-atomic_try_cmpxchg-in-__get_reqs_available.patch
