On 22.05.25 05:49, lizhe.67@xxxxxxxxxxxxx wrote:
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;
+}
What might be faster is obtaining the folio, and then calculating the
next expected page pointer, comparing whether the page pointers match.
Essentially, using folio_page() to calculate the expected next page.
nth_page() is a simple pointer arithmetic with CONFIG_SPARSEMEM_VMEMMAP,
so that might be rather fast.
So we'd obtain
start_idx = folio_idx(folio, batch->pages[batch->offset]);
and then check for
batch->pages[batch->offset + i] == folio_page(folio, start_idx + i)
--
Cheers,
David / dhildenb
