From: Baolu Lu baolu.lu@linux.intel.com Sent: Saturday, February 4, 2023 2:32 PM
On 2023/2/4 7:04, Jacob Pan wrote:
Intel IOMMU driver implements IOTLB flush queue with domain selective or PASID selective invalidations. In this case there's no need to track IOVA page range and sync IOTLBs, which may cause significant
performance
hit.
[Add cc Robin]
If I understand this patch correctly, this might be caused by below helper:
/**
- iommu_iotlb_gather_add_page - Gather for page-based TLB invalidation
- @domain: IOMMU domain to be invalidated
- @gather: TLB gather data
- @iova: start of page to invalidate
- @size: size of page to invalidate
- Helper for IOMMU drivers to build invalidation commands based on
individual
- pages, or with page size/table level hints which cannot be gathered
if they
- differ.
*/ static inline void iommu_iotlb_gather_add_page(struct iommu_domain *domain, struct iommu_iotlb_gather *gather, unsigned long iova, size_t size) { /* * If the new page is disjoint from the current range or is mapped at * a different granularity, then sync the TLB so that the gather * structure can be rewritten. */ if ((gather->pgsize && gather->pgsize != size) || iommu_iotlb_gather_is_disjoint(gather, iova, size)) iommu_iotlb_sync(domain, gather);
gather->pgsize = size; iommu_iotlb_gather_add_range(gather, iova, size);}
As the comments for iommu_iotlb_gather_is_disjoint() says,
"...For many IOMMUs, flushing the IOMMU in this case is better than merging the two, which might lead to unnecessary invalidations. ..."
So, perhaps the right fix for this performance issue is to add
if (!gather->queued)
in iommu_iotlb_gather_add_page() or iommu_iotlb_gather_is_disjoint()? It should benefit other arch's as well.
There are only two callers of this helper: intel and arm-smmu-v3.
Looks other drivers just implements direct flush via io_pgtable_tlb_add_page().
and their unmap callback typically does:
if (!iommu_iotlb_gather_queued(gather)) io_pgtable_tlb_add_page();
from this angle it's same policy as Jacob's does, i.e. if it's already queued then no need to further call optimization for direct flush.