Let's move out the is_kdump_kernel() check from iommu_dma_deferred_attach()
to iommu_dma_init(), and use the static-key in the fast-path to minimize
the impact in the normal case.
Signed-off-by: Lianbo Jiang <[email protected]>
Co-developed-by: Robin Murphy <[email protected]>
Signed-off-by: Robin Murphy <[email protected]>
---
drivers/iommu/dma-iommu.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)
diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index f0305e6aac1b..3711b4a6e4f9 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -51,6 +51,8 @@ struct iommu_dma_cookie {
struct iommu_domain *fq_domain;
};
+static DEFINE_STATIC_KEY_FALSE(__deferred_attach);
+
void iommu_dma_free_cpu_cached_iovas(unsigned int cpu,
struct iommu_domain *domain)
{
@@ -383,9 +385,6 @@ static int iommu_dma_deferred_attach(struct device *dev,
{
const struct iommu_ops *ops = domain->ops;
- if (!is_kdump_kernel())
- return 0;
-
if (unlikely(ops->is_attach_deferred &&
ops->is_attach_deferred(domain, dev)))
return iommu_attach_device(domain, dev);
@@ -535,7 +534,8 @@ static dma_addr_t __iommu_dma_map(struct device *dev, phys_addr_t phys,
size_t iova_off = iova_offset(iovad, phys);
dma_addr_t iova;
- if (unlikely(iommu_dma_deferred_attach(dev, domain)))
+ if (static_branch_unlikely(&__deferred_attach) &&
+ iommu_dma_deferred_attach(dev, domain))
return DMA_MAPPING_ERROR;
size = iova_align(iovad, size + iova_off);
@@ -693,7 +693,8 @@ static void *iommu_dma_alloc_remap(struct device *dev, size_t size,
*dma_handle = DMA_MAPPING_ERROR;
- if (unlikely(iommu_dma_deferred_attach(dev, domain)))
+ if (static_branch_unlikely(&__deferred_attach) &&
+ iommu_dma_deferred_attach(dev, domain))
return NULL;
min_size = alloc_sizes & -alloc_sizes;
@@ -1003,7 +1004,8 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg,
unsigned long mask = dma_get_seg_boundary(dev);
int i;
- if (unlikely(iommu_dma_deferred_attach(dev, domain)))
+ if (static_branch_unlikely(&__deferred_attach) &&
+ iommu_dma_deferred_attach(dev, domain))
return 0;
if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
@@ -1451,6 +1453,9 @@ void iommu_dma_compose_msi_msg(struct msi_desc *desc,
static int iommu_dma_init(void)
{
+ if (is_kdump_kernel())
+ static_branch_enable(&__deferred_attach);
+
return iova_cache_get();
}
arch_initcall(iommu_dma_init);
--
2.17.1
On Tue, Jan 19, 2021 at 07:16:15PM +0800, Lianbo Jiang wrote:
> +static DEFINE_STATIC_KEY_FALSE(__deferred_attach);
Why the strange underscores? Wouldn't iommu_deferred_attach_enabled
be a better name?
> - if (unlikely(iommu_dma_deferred_attach(dev, domain)))
> + if (static_branch_unlikely(&__deferred_attach) &&
> + iommu_dma_deferred_attach(dev, domain))
Also insted of duplicating this logic in three places, maybe rename
iommu_dma_deferred_attach to __iommu_dma_deferred_attach and create
a small inline wrapper for it?
On 2021-01-19 15:26, Christoph Hellwig wrote:
> On Tue, Jan 19, 2021 at 07:16:15PM +0800, Lianbo Jiang wrote:
>> +static DEFINE_STATIC_KEY_FALSE(__deferred_attach);
>
> Why the strange underscores? Wouldn't iommu_deferred_attach_enabled
> be a better name?
>
>> - if (unlikely(iommu_dma_deferred_attach(dev, domain)))
>> + if (static_branch_unlikely(&__deferred_attach) &&
>> + iommu_dma_deferred_attach(dev, domain))
>
> Also insted of duplicating this logic in three places, maybe rename
> iommu_dma_deferred_attach to __iommu_dma_deferred_attach and create
> a small inline wrapper for it?
Once patch #2 is in place, I really don't see any point. The "helper"
would add a minimum of 5 lines to save at most 3, and would have to be
annotated as always_inline - which a whole other camp of people would
probably object to - in order for the static branch to be properly useful.
It's not as if this is a complex or hard-to-read expression, so IMO
having 3 lines repeated 3 times is objectively better than having 2
lines necessarily repeated 3 times plus having to scroll up and find
several more lines to follow what it's doing.
Robin.
Hi, Christoph
Thanks for the comment.
在 2021年01月19日 23:26, Christoph Hellwig 写道:
> On Tue, Jan 19, 2021 at 07:16:15PM +0800, Lianbo Jiang wrote:
>> +static DEFINE_STATIC_KEY_FALSE(__deferred_attach);
> Why the strange underscores? Wouldn't iommu_deferred_attach_enabled
The variable is defined with the static keyword, which indicates that the
variable is only used in the local module(file), and gives a hint explicitly
with the underscore prefix. Anyway, this is my personal opinion.
> be a better name?
>
It could be a long name?
Thanks.
Lianbo