On 2020-08-27 09:43, Shaokun Zhang wrote:
From: Yuqi Jin <jiny...@huawei.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.
Looks reasonable to me - the "compare" part is already covered by the
separate atomic_read(), and as you say there's no harm if the "exchange"
part races as long as it's still atomic.
Reviewed-by: Robin Murphy <robin.mur...@arm.com>
Cc: Joerg Roedel <j...@8bytes.org>
Signed-off-by: Yuqi Jin <jiny...@huawei.com>
Signed-off-by: Shaokun Zhang <zhangshao...@hisilicon.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));
}
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