Hi Eugenio, > -----Original Message----- > From: Eugenio Pérez <epere...@redhat.com> > Sent: Saturday, August 28, 2021 12:13 AM > To: Maxime Coquelin <maxime.coque...@redhat.com>; Xia, Chenbo > <chenbo....@intel.com> > Cc: dev@dpdk.org; Pei Zhang <pezh...@redhat.com>; Jason Wang > <jasow...@redhat.com> > Subject: [PATCH] vhost: Clean iotlb cache on vring stop
Clean -> clean > > Old IOVA cache entries are left when there is a change on virtio driver > in VM. In case that all these old entries have iova addresses lesser > than new iova entries, vhost code will need to iterate all the cache to > find the new ones. In case of just a new iova entry needed for the new > translations, this condition will last forever. > > This has been observed in virtio-net to testpmd's vfio-pci driver > transition, reducing the performance from more than 10Mpps to less than > 0.07Mpps if the hugepage address was higher than the networking > buffers. Since all new buffers are contained in this new gigantic page, > vhost needs to scan IOTLB_CACHE_SIZE - 1 for each translation at worst. I'm curious why QEMU will not invalidate iotlb when virtio-net driver is removed (dma region should be unmapped). And since the perf drop is huge, why not cc to stable and add fix tag? Thanks, Chenbo > > Signed-off-by: Eugenio Pérez <epere...@redhat.com> > Reported-by: Pei Zhang <pezh...@redhat.com> > --- > lib/vhost/vhost_user.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c > index 29a4c9af60..7de48f5333 100644 > --- a/lib/vhost/vhost_user.c > +++ b/lib/vhost/vhost_user.c > @@ -2113,6 +2113,8 @@ vhost_user_get_vring_base(struct virtio_net **pdev, > msg->size = sizeof(msg->payload.state); > msg->fd_num = 0; > > + vhost_user_iotlb_flush_all(vq); > + > vring_invalidate(dev, vq); > > return RTE_VHOST_MSG_RESULT_REPLY; > -- > 2.27.0
