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Commit c5e66887 authored by Alex Williamson's avatar Alex Williamson
Browse files

vfio/type1: Add conditional rescheduling 



IOMMU operations can be expensive and it's not very difficult for a
user to give us a lot of work to do for a map or unmap operation.
Killing a large VM will vfio assigned devices can result in soft
lockups and IOMMU tracing shows that we can easily spend 80% of our
time with need-resched set.  A sprinkling of conf_resched() calls
after map and unmap calls has a very tiny affect on performance
while resulting in traces with <1% of calls overflowing into needs-
resched.

Signed-off-by: default avatarAlex Williamson <alex.williamson@redhat.com>
parent babbf176

drivers/vfio/vfio_iommu_type1.c

+7 −1
Original line number Diff line number Diff line
@@ -351,8 +351,10 @@ static void vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma) 
	domain = d = list_first_entry(&iommu->domain_list,

				      struct vfio_domain, next);



	list_for_each_entry_continue(d, &iommu->domain_list, next)

	list_for_each_entry_continue(d, &iommu->domain_list, next) {

		iommu_unmap(d->domain, dma->iova, dma->size);

		cond_resched();

	}



	while (iova < end) {

		size_t unmapped, len;
@@ -384,6 +386,8 @@ static void vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma) 
					     unmapped >> PAGE_SHIFT,

					     dma->prot, false);

		iova += unmapped;



		cond_resched();

	}



	vfio_lock_acct(-unlocked);
@@ -528,6 +532,8 @@ static int vfio_iommu_map(struct vfio_iommu *iommu, dma_addr_t iova, 
			    map_try_harder(d, iova, pfn, npage, prot))

				goto unwind;

		}



		cond_resched();

	}



	return 0;