From: Yuqi Jin <[email protected]>
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 <[email protected]>
Signed-off-by: Yuqi Jin <[email protected]>
Signed-off-by: Shaokun Zhang <[email protected]>
---
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
On 2020-08-27 09:43, Shaokun Zhang wrote:
> From: Yuqi Jin <[email protected]>
>
> 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 <[email protected]>
> Cc: Joerg Roedel <[email protected]>
> Signed-off-by: Yuqi Jin <[email protected]>
> Signed-off-by: Shaokun Zhang <[email protected]>
> ---
> 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));
> }
>
Adding Robin.
On Thu, Aug 27, 2020 at 04:43:54PM +0800, Shaokun Zhang wrote:
> From: Yuqi Jin <[email protected]>
>
> 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 <[email protected]>
> Signed-off-by: Yuqi Jin <[email protected]>
> Signed-off-by: Shaokun Zhang <[email protected]>
> ---
> 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
Hi Joerg,
On 2020-09-04 10:37, Joerg Roedel wrote:
> Adding Robin.
Did you miss that I've reviewed this already? :)
https://lore.kernel.org/linux-iommu/[email protected]/
Robin.
> On Thu, Aug 27, 2020 at 04:43:54PM +0800, Shaokun Zhang wrote:
>> From: Yuqi Jin <[email protected]>
>>
>> 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 <[email protected]>
>> Signed-off-by: Yuqi Jin <[email protected]>
>> Signed-off-by: Shaokun Zhang <[email protected]>
>> ---
>> 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
> _______________________________________________
> iommu mailing list
> [email protected]
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
>
Hi Robin,
On Fri, Sep 04, 2020 at 10:58:14AM +0100, Robin Murphy wrote:
> On 2020-09-04 10:37, Joerg Roedel wrote:
> > Adding Robin.
>
> Did you miss that I've reviewed this already? :)
>
> https://lore.kernel.org/linux-iommu/[email protected]/
Hmm, that mail wasn't in my inbox, but b4 found it. I'll need to look
why it didn't make it...
Joerg