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[37.44.92.89]) by smtp.gmail.com with ESMTPSA id z9sm294677lfa.25.2019.05.23.08.39.26 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 23 May 2019 08:39:27 -0700 (PDT) From: "Pavel Begunkov (Silence)" To: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Pavel Begunkov Subject: [PATCH 1/1] sbitmap: Replace cmpxchg with xchg Date: Thu, 23 May 2019 18:39:16 +0300 Message-Id: <722e1d561f0a49dc464d3a2b1be4c077f7502726.1558625912.git.asml.silence@gmail.com> X-Mailer: git-send-email 2.21.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Pavel Begunkov cmpxchg() with an immediate value could be replaced with less expensive xchg(). The same true if new value don't _depend_ on the old one. In the second block, atomic_cmpxchg() return value isn't checked, so after atomic_cmpxchg() -> atomic_xchg() conversion it could be replaced with atomic_set(). Comparison with atomic_read() in the second chunk was left as an optimisation (if that was the initial intention). Signed-off-by: Pavel Begunkov --- lib/sbitmap.c | 10 +++------- 1 file changed, 3 insertions(+), 7 deletions(-) diff --git a/lib/sbitmap.c b/lib/sbitmap.c index 155fe38756ec..7d7e0e278523 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -37,9 +37,7 @@ static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index) /* * First get a stable cleared mask, setting the old mask to 0. */ - do { - mask = sb->map[index].cleared; - } while (cmpxchg(&sb->map[index].cleared, mask, 0) != mask); + mask = xchg(&sb->map[index].cleared, 0); /* * Now clear the masked bits in our free word @@ -527,10 +525,8 @@ static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq) struct sbq_wait_state *ws = &sbq->ws[wake_index]; if (waitqueue_active(&ws->wait)) { - int o = atomic_read(&sbq->wake_index); - - if (wake_index != o) - atomic_cmpxchg(&sbq->wake_index, o, wake_index); + if (wake_index != atomic_read(&sbq->wake_index)) + atomic_set(&sbq->wake_index, wake_index); return ws; } -- 2.21.0