linux-kernel - [PATCH] iommu/iova: Replace cmpxchg with xchg in queue

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Date:   Thu, 27 Aug 2020 16:43:54 +0800
From:   Shaokun Zhang <zhangshaokun@...ilicon.com>
To:     <iommu@...ts.linux-foundation.org>, <linux-kernel@...r.kernel.org>
CC:     Yuqi Jin <jinyuqi@...wei.com>, Joerg Roedel <joro@...tes.org>,
        "Shaokun Zhang" <zhangshaokun@...ilicon.com>
Subject: [PATCH] iommu/iova: Replace cmpxchg with xchg in queue_iova

From: Yuqi Jin <jinyuqi@...wei.com>

The performance of the atomic_xchg is better than atomic_cmpxchg because
no comparison is required. While the value of @fq_timer_on can only be 0
or 1. Let's use atomic_xchg instead of atomic_cmpxchg here because we
only need to check that the value changes from 0 to 1 or from 1 to 1.

Cc: Joerg Roedel <joro@...tes.org>
Signed-off-by: Yuqi Jin <jinyuqi@...wei.com>
Signed-off-by: Shaokun Zhang <zhangshaokun@...ilicon.com>
---
 drivers/iommu/iova.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index 45a251da5453..30d969a4c5fd 100644
--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -579,7 +579,7 @@ void queue_iova(struct iova_domain *iovad,
 
 	/* Avoid false sharing as much as possible. */
 	if (!atomic_read(&iovad->fq_timer_on) &&
-	    !atomic_cmpxchg(&iovad->fq_timer_on, 0, 1))
+	    !atomic_xchg(&iovad->fq_timer_on, 1))
 		mod_timer(&iovad->fq_timer,
 			  jiffies + msecs_to_jiffies(IOVA_FQ_TIMEOUT));
 }
-- 
2.7.4