On 26.06.2023 18:36, Stefano Garzarella wrote:
> On Sat, Jun 03, 2023 at 11:49:25PM +0300, Arseniy Krasnov wrote:
>> For non-linear skb use its pages from fragment array as buffers in
>> virtio tx queue. These pages are already pinned by 'get_user_pages()'
>> during such skb creation.
>>
>> Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
>> ---
>> net/vmw_vsock/virtio_transport.c | 37 ++++++++++++++++++++++++++------
>> 1 file changed, 31 insertions(+), 6 deletions(-)
>>
>> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>> index e95df847176b..6053d8341091 100644
>> --- a/net/vmw_vsock/virtio_transport.c
>> +++ b/net/vmw_vsock/virtio_transport.c
>> @@ -100,7 +100,9 @@ virtio_transport_send_pkt_work(struct work_struct *work)
>> vq = vsock->vqs[VSOCK_VQ_TX];
>>
>> for (;;) {
>> - struct scatterlist hdr, buf, *sgs[2];
>> + /* +1 is for packet header. */
>> + struct scatterlist *sgs[MAX_SKB_FRAGS + 1];
>> + struct scatterlist bufs[MAX_SKB_FRAGS + 1];
>> int ret, in_sg = 0, out_sg = 0;
>> struct sk_buff *skb;
>> bool reply;
>> @@ -111,12 +113,35 @@ virtio_transport_send_pkt_work(struct work_struct *work)
>>
>> virtio_transport_deliver_tap_pkt(skb);
>> reply = virtio_vsock_skb_reply(skb);
>> + sg_init_one(&bufs[0], virtio_vsock_hdr(skb), sizeof(*virtio_vsock_hdr(skb)));
>> + sgs[out_sg++] = &bufs[0];
>
> Can we use out_sg also to index bufs (here and in the rest of the code)?
>
> E.g.
>
> sg_init_one(&bufs[out_sg], ...)
> sgs[out_sg] = &bufs[out_sg];
> ++out_sg;
>
> ...
> if (skb->len > 0) {
> sg_init_one(&bufs[out_sg], skb->data, skb->len);
> sgs[out_sg] = &bufs[out_sg];
> ++out_sg;
> }
>
> etc...
>
>> +
>
> For readability, I would move the smaller branch above:
>
> if (!skb_is_nonlinear(skb)) {
> // small block
> ...
> } else {
> // big block
> ...
> }
>
>> + if (skb_is_nonlinear(skb)) {
>> + struct skb_shared_info *si;
>> + int i;
>> +
>> + si = skb_shinfo(skb);
>> +
>> + for (i = 0; i < si->nr_frags; i++) {
>> + skb_frag_t *skb_frag = &si->frags[i];
>> + void *va = page_to_virt(skb_frag->bv_page);
>> +
>> + /* We will use 'page_to_virt()' for userspace page here,
>> + * because virtio layer will call 'virt_to_phys()' later
>> + * to fill buffer descriptor. We don't touch memory at
>> + * "virtual" address of this page.
>> + */
>> + sg_init_one(&bufs[i + 1],
>> + va + skb_frag->bv_offset,
>> + skb_frag->bv_len);
>> + sgs[out_sg++] = &bufs[i + 1];
>> + }
>> + } else {
>> + if (skb->len > 0) {
>
> Should we do the same check (skb->len > 0) for nonlinear skb as well?
> Or do the nonlinear ones necessarily have len > 0?
Yes, non-linear skb always has 'data_len' > 0, e.g. such skbs always have some
data in it.
Thanks, Arseniy
>
>> + sg_init_one(&bufs[1], skb->data, skb->len);
>> + sgs[out_sg++] = &bufs[1];
>> + }
>>
> ^
> Blank line that we can remove.
>
> Stefano
>
>> - sg_init_one(&hdr, virtio_vsock_hdr(skb), sizeof(*virtio_vsock_hdr(skb)));
>> - sgs[out_sg++] = &hdr;
>> - if (skb->len > 0) {
>> - sg_init_one(&buf, skb->data, skb->len);
>> - sgs[out_sg++] = &buf;
>> }
>>
>> ret = virtqueue_add_sgs(vq, sgs, out_sg, in_sg, skb, GFP_KERNEL);
>> --
>> 2.25.1
>>
>
