Re: [PATCH] iommu/iova: Replace cmpxchg with xchg in queue_iova
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/3afcc7b2-0bfb-b79c-513f-1beb66c5f...@arm.com/ Hmm, that mail wasn't in my inbox, but b4 found it. I'll need to look why it didn't make it... Joerg ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH] iommu/iova: Replace cmpxchg with xchg in queue_iova
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/3afcc7b2-0bfb-b79c-513f-1beb66c5f...@arm.com/ Robin. On Thu, Aug 27, 2020 at 04:43:54PM +0800, Shaokun Zhang wrote: From: Yuqi Jin 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 Signed-off-by: Yuqi Jin Signed-off-by: Shaokun Zhang --- 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(>fq_timer_on) && - !atomic_cmpxchg(>fq_timer_on, 0, 1)) + !atomic_xchg(>fq_timer_on, 1)) mod_timer(>fq_timer, jiffies + msecs_to_jiffies(IOVA_FQ_TIMEOUT)); } -- 2.7.4 ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH] iommu/iova: Replace cmpxchg with xchg in queue_iova
Adding Robin. On Thu, Aug 27, 2020 at 04:43:54PM +0800, Shaokun Zhang wrote: > From: Yuqi Jin > > 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 > Signed-off-by: Yuqi Jin > Signed-off-by: Shaokun Zhang > --- > 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(>fq_timer_on) && > - !atomic_cmpxchg(>fq_timer_on, 0, 1)) > + !atomic_xchg(>fq_timer_on, 1)) > mod_timer(>fq_timer, > jiffies + msecs_to_jiffies(IOVA_FQ_TIMEOUT)); > } > -- > 2.7.4 ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH] iommu/iova: Replace cmpxchg with xchg in queue_iova
On 2020-08-27 09:43, Shaokun Zhang wrote: From: Yuqi Jin 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 Cc: Joerg Roedel Signed-off-by: Yuqi Jin Signed-off-by: Shaokun Zhang --- 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(>fq_timer_on) && - !atomic_cmpxchg(>fq_timer_on, 0, 1)) + !atomic_xchg(>fq_timer_on, 1)) mod_timer(>fq_timer, jiffies + msecs_to_jiffies(IOVA_FQ_TIMEOUT)); } ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
[PATCH] iommu/iova: Replace cmpxchg with xchg in queue_iova
From: Yuqi Jin 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 Signed-off-by: Yuqi Jin Signed-off-by: Shaokun Zhang --- 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(>fq_timer_on) && - !atomic_cmpxchg(>fq_timer_on, 0, 1)) + !atomic_xchg(>fq_timer_on, 1)) mod_timer(>fq_timer, jiffies + msecs_to_jiffies(IOVA_FQ_TIMEOUT)); } -- 2.7.4 ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
