Date:   Wed, 13 Apr 2022 15:04:10 +0800
From:   Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Jeff Dike <jdike@...toit.com>, Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        Vadim Pasternak <vadimp@...dia.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Cornelia Huck <cohuck@...hat.com>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Johannes Berg <johannes.berg@...el.com>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        linux-um@...ts.infradead.org, netdev@...r.kernel.org,
        platform-driver-x86@...r.kernel.org,
        linux-remoteproc@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, bpf@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v9 09/32] virtio_ring: split: extract the logic of vq init

On Tue, 12 Apr 2022 11:42:25 +0800, Jason Wang <jasowang@...hat.com> wrote:
>
> 在 2022/4/6 上午11:43, Xuan Zhuo 写道:
> > Separate the logic of initializing vq, and subsequent patches will call
> > it separately.
> >
> > The feature of this part is that it does not depend on the information
> > passed by the upper layer and can be called repeatedly.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > ---
> >   drivers/virtio/virtio_ring.c | 68 ++++++++++++++++++++----------------
> >   1 file changed, 38 insertions(+), 30 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index 083f2992ba0d..874f878087a3 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -916,6 +916,43 @@ static void *virtqueue_detach_unused_buf_split(struct virtqueue *_vq)
> >   	return NULL;
> >   }
> >
> > +static void vring_virtqueue_init_split(struct vring_virtqueue *vq,
> > +				       struct virtio_device *vdev,
> > +				       bool own_ring)
> > +{
> > +	vq->packed_ring = false;
> > +	vq->vq.num_free = vq->split.vring.num;
> > +	vq->we_own_ring = own_ring;
> > +	vq->broken = false;
> > +	vq->last_used_idx = 0;
> > +	vq->event_triggered = false;
> > +	vq->num_added = 0;
> > +	vq->use_dma_api = vring_use_dma_api(vdev);
> > +#ifdef DEBUG
> > +	vq->in_use = false;
> > +	vq->last_add_time_valid = false;
> > +#endif
> > +
> > +	vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
> > +
> > +	if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
> > +		vq->weak_barriers = false;
> > +
> > +	vq->split.avail_flags_shadow = 0;
> > +	vq->split.avail_idx_shadow = 0;
> > +
> > +	/* No callback?  Tell other side not to bother us. */
> > +	if (!vq->vq.callback) {
> > +		vq->split.avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
> > +		if (!vq->event)
> > +			vq->split.vring.avail->flags = cpu_to_virtio16(vdev,
> > +					vq->split.avail_flags_shadow);
> > +	}
> > +
> > +	/* Put everything in free lists. */
> > +	vq->free_head = 0;
>
>
> It's not clear what kind of initialization that we want to do here. E.g
> it mixes split specific setups with some general setups which is kind of
> duplication of vring_virtqueue_init_packed().
>
> I wonder if it's better to only do split specific setups here and have a
> common helper to do the setup that is irrelevant to ring layout.

Yes, you are right, I didn't notice this situation before.

Thanks.

>
> Thanks
>
>
> > +}
> > +
> >   static void vring_virtqueue_attach_split(struct vring_virtqueue *vq,
> >   					 struct vring vring,
> >   					 struct vring_desc_state_split *desc_state,
> > @@ -2249,42 +2286,15 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
> >   	if (!vq)
> >   		return NULL;
> >
> > -	vq->packed_ring = false;
> >   	vq->vq.callback = callback;
> >   	vq->vq.vdev = vdev;
> >   	vq->vq.name = name;
> > -	vq->vq.num_free = vring.num;
> >   	vq->vq.index = index;
> > -	vq->we_own_ring = false;
> >   	vq->notify = notify;
> >   	vq->weak_barriers = weak_barriers;
> > -	vq->broken = false;
> > -	vq->last_used_idx = 0;
> > -	vq->event_triggered = false;
> > -	vq->num_added = 0;
> > -	vq->use_dma_api = vring_use_dma_api(vdev);
> > -#ifdef DEBUG
> > -	vq->in_use = false;
> > -	vq->last_add_time_valid = false;
> > -#endif
> >
> >   	vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC) &&
> >   		!context;
> > -	vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
> > -
> > -	if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
> > -		vq->weak_barriers = false;
> > -
> > -	vq->split.avail_flags_shadow = 0;
> > -	vq->split.avail_idx_shadow = 0;
> > -
> > -	/* No callback?  Tell other side not to bother us. */
> > -	if (!callback) {
> > -		vq->split.avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
> > -		if (!vq->event)
> > -			vq->split.vring.avail->flags = cpu_to_virtio16(vdev,
> > -					vq->split.avail_flags_shadow);
> > -	}
> >
> >   	err = vring_alloc_state_extra_split(vring.num, &state, &extra);
> >   	if (err) {
> > @@ -2293,9 +2303,7 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
> >   	}
> >
> >   	vring_virtqueue_attach_split(vq, vring, state, extra);
> > -
> > -	/* Put everything in free lists. */
> > -	vq->free_head = 0;
> > +	vring_virtqueue_init_split(vq, vdev, false);
> >
> >   	spin_lock(&vdev->vqs_list_lock);
> >   	list_add_tail(&vq->vq.list, &vdev->vqs);
>

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