On Mon, Jun 08, 2020 at 11:35:40AM +0800, Jason Wang wrote: > > On 2020/6/7 下午9:57, Michael S. Tsirkin wrote: > > On Fri, Jun 05, 2020 at 11:40:17AM +0800, Jason Wang wrote: > > > On 2020/6/4 下午4:59, Michael S. Tsirkin wrote: > > > > On Wed, Jun 03, 2020 at 03:27:39PM +0800, Jason Wang wrote: > > > > > On 2020/6/2 下午9:06, Michael S. Tsirkin wrote: > > > > > > With this patch applied, new and old code perform identically. > > > > > > > > > > > > Lots of extra optimizations are now possible, e.g. > > > > > > we can fetch multiple heads with copy_from/to_user now. > > > > > > We can get rid of maintaining the log array. Etc etc. > > > > > > > > > > > > Signed-off-by: Michael S. Tsirkin<mst@xxxxxxxxxx> > > > > > > Signed-off-by: Eugenio Pérez<eperezma@xxxxxxxxxx> > > > > > > Link:https://lore.kernel.org/r/20200401183118.8334-4-eperezma@xxxxxxxxxx > > > > > > Signed-off-by: Michael S. Tsirkin<mst@xxxxxxxxxx> > > > > > > --- > > > > > > drivers/vhost/test.c | 2 +- > > > > > > drivers/vhost/vhost.c | 47 ++++++++++++++++++++++++++++++++++++++----- > > > > > > drivers/vhost/vhost.h | 5 ++++- > > > > > > 3 files changed, 47 insertions(+), 7 deletions(-) > > > > > > > > > > > > diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c > > > > > > index 9a3a09005e03..02806d6f84ef 100644 > > > > > > --- a/drivers/vhost/test.c > > > > > > +++ b/drivers/vhost/test.c > > > > > > @@ -119,7 +119,7 @@ static int vhost_test_open(struct inode *inode, struct file *f) > > > > > > dev = &n->dev; > > > > > > vqs[VHOST_TEST_VQ] = &n->vqs[VHOST_TEST_VQ]; > > > > > > n->vqs[VHOST_TEST_VQ].handle_kick = handle_vq_kick; > > > > > > - vhost_dev_init(dev, vqs, VHOST_TEST_VQ_MAX, UIO_MAXIOV, > > > > > > + vhost_dev_init(dev, vqs, VHOST_TEST_VQ_MAX, UIO_MAXIOV + 64, > > > > > > VHOST_TEST_PKT_WEIGHT, VHOST_TEST_WEIGHT, NULL); > > > > > > f->private_data = n; > > > > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > > > > index 8f9a07282625..aca2a5b0d078 100644 > > > > > > --- a/drivers/vhost/vhost.c > > > > > > +++ b/drivers/vhost/vhost.c > > > > > > @@ -299,6 +299,7 @@ static void vhost_vq_reset(struct vhost_dev *dev, > > > > > > { > > > > > > vq->num = 1; > > > > > > vq->ndescs = 0; > > > > > > + vq->first_desc = 0; > > > > > > vq->desc = NULL; > > > > > > vq->avail = NULL; > > > > > > vq->used = NULL; > > > > > > @@ -367,6 +368,11 @@ static int vhost_worker(void *data) > > > > > > return 0; > > > > > > } > > > > > > +static int vhost_vq_num_batch_descs(struct vhost_virtqueue *vq) > > > > > > +{ > > > > > > + return vq->max_descs - UIO_MAXIOV; > > > > > > +} > > > > > 1 descriptor does not mean 1 iov, e.g userspace may pass several 1 byte > > > > > length memory regions for us to translate. > > > > > > > > > Yes but I don't see the relevance. This tells us how many descriptors to > > > > batch, not how many IOVs. > > > Yes, but questions are: > > > > > > - this introduce another obstacle to support more than 1K queue size > > > - if we support 1K queue size, does it mean we need to cache 1K descriptors, > > > which seems a large stress on the cache > > > > > > Thanks > > > > > > > > Still don't understand the relevance. We support up to 1K descriptors > > per buffer just for IOV since we always did. This adds 64 more > > descriptors - is that a big deal? > > > If I understanding correctly, for net, the code tries to batch descriptors > for at last one packet. > > If we allow 1K queue size then we allow a packet that consists of 1K > descriptors. Then we need to cache 1K descriptors. > > Thanks That case is already so pathological, I am not at all worried about it performing well. -- MST
