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 35c9008..57d8c37 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -351,8 +351,10 @@
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 @@
unmapped >> PAGE_SHIFT,
dma->prot, false);
iova += unmapped;
+
+ cond_resched();
}
vfio_lock_acct(-unlocked);
@@ -528,6 +532,8 @@
map_try_harder(d, iova, pfn, npage, prot))
goto unwind;
}
+
+ cond_resched();
}
return 0;