On Thu, Jan 13, 2022 at 10:57 PM Stefano Garzarella <sgarzare@xxxxxxxxxx> wrote: > > In vhost_enable_notify() we enable the notifications and we read > the avail index to check if new buffers have become available in > the meantime. In this case, the device would go to re-read avail > index to access the descriptor. > > As we already do in other place, we can cache the value in `avail_idx` > and compare it with `last_avail_idx` to check if there are new > buffers available. > > Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx> Patch looks fine but I guess we won't get performance improvement since it doesn't save any userspace/VM memory access? Thanks > --- > drivers/vhost/vhost.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 59edb5a1ffe2..07363dff559e 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -2543,8 +2543,9 @@ bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq) > &vq->avail->idx, r); > return false; > } > + vq->avail_idx = vhost16_to_cpu(vq, avail_idx); > > - return vhost16_to_cpu(vq, avail_idx) != vq->avail_idx; > + return vq->avail_idx != vq->last_avail_idx; > } > EXPORT_SYMBOL_GPL(vhost_enable_notify); > > -- > 2.31.1 >
