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aio: use atomic_try_cmpxchg in __get_reqs_available 

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@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Uros Bizjak 2022-07-14 18:48:51 +02:00 committed by Andrew Morton
parent b0192296b4
commit 38ace0d513
1 changed files with 3 additions and 6 deletions
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9
fs/aio.c
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@ -951,16 +951,13 @@ static bool __get_reqs_available(struct kioctx *ctx)
local_irq_save(flags); local_irq_save(flags);
kcpu = this_cpu_ptr(ctx->cpu); kcpu = this_cpu_ptr(ctx->cpu);
if (!kcpu->reqs_available) { if (!kcpu->reqs_available) {
int old, avail = atomic_read(&ctx->reqs_available); int avail = atomic_read(&ctx->reqs_available);
do { do {
if (avail < ctx->req_batch) if (avail < ctx->req_batch)
goto out; goto out;
} while (!atomic_try_cmpxchg(&ctx->reqs_available,
old = avail; &avail, avail - ctx->req_batch));
avail = atomic_cmpxchg(&ctx->reqs_available,
avail, avail - ctx->req_batch);
} while (avail != old);
kcpu->reqs_available += ctx->req_batch; kcpu->reqs_available += ctx->req_batch;
} }