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 <[email protected]> --- drivers/vfio/vfio_iommu_type1.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c index 35c9008..57d8c37 100644 --- 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; -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
