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: Alex Williamson <alex.williamson@redhat.com>

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 35c90089478ebc3b70488eb8accaa6b7ed88431e..57d8c37a002b0e0b8d49891536b8ddfab64afc6b 100644 (file)
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -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;