On Wed, 21 May 2025 13:17:11 -0600, alex.williamson@xxxxxxxxxx wrote:
>> From: Li Zhe <lizhe.67@xxxxxxxxxxxxx>
>>
>> When vfio_pin_pages_remote() is called with a range of addresses that
>> includes large folios, the function currently performs individual
>> statistics counting operations for each page. This can lead to significant
>> performance overheads, especially when dealing with large ranges of pages.
>>
>> This patch optimize this process by batching the statistics counting
>> operations.
>>
>> The performance test results for completing the 8G VFIO IOMMU DMA mapping,
>> obtained through trace-cmd, are as follows. In this case, the 8G virtual
>> address space has been mapped to physical memory using hugetlbfs with
>> pagesize=2M.
>>
>> Before this patch:
>> funcgraph_entry: # 33813.703 us | vfio_pin_map_dma();
>>
>> After this patch:
>> funcgraph_entry: # 16071.378 us | vfio_pin_map_dma();
>>
>> Signed-off-by: Li Zhe <lizhe.67@xxxxxxxxxxxxx>
>> Co-developed-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
>> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
>> ---
>
>Given the discussion on v3, this is currently a Nak. Follow-up in that
>thread if there are further ideas how to salvage this. Thanks,
How about considering the solution David mentioned to check whether the
pages or PFNs are actually consecutive?
I have conducted a preliminary attempt, and the performance testing
revealed that the time consumption is approximately 18,000 microseconds.
Compared to the previous 33,000 microseconds, this also represents a
significant improvement.
The modification is quite straightforward. The code below reflects the
changes I have made based on this patch.
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index bd46ed9361fe..1cc1f76d4020 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -627,6 +627,19 @@ static long vaddr_get_pfns(struct mm_struct *mm, unsigned long vaddr,
return ret;
}
+static inline long continuous_page_num(struct vfio_batch *batch, long npage)
+{
+ long i;
+ unsigned long next_pfn = page_to_pfn(batch->pages[batch->offset]) + 1;
+
+ for (i = 1; i < npage; ++i) {
+ if (page_to_pfn(batch->pages[batch->offset + i]) != next_pfn)
+ break;
+ next_pfn++;
+ }
+ return i;
+}
+
/*
* Attempt to pin pages. We really don't want to track all the pfns and
* the iommu can only map chunks of consecutive pfns anyway, so get the
@@ -708,8 +721,12 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
*/
nr_pages = min_t(long, batch->size, folio_nr_pages(folio) -
folio_page_idx(folio, batch->pages[batch->offset]));
- if (nr_pages > 1 && vfio_find_vpfn_range(dma, iova, nr_pages))
- nr_pages = 1;
+ if (nr_pages > 1) {
+ if (vfio_find_vpfn_range(dma, iova, nr_pages))
+ nr_pages = 1;
+ else
+ nr_pages = continuous_page_num(batch, nr_pages);
+ }
/*
* Reserved pages aren't counted against the user,
Thanks,
Zhe
