Re: [RFC PATCH v4 03/17] vsock/virtio: support to send non-linear skb
From: Stefano Garzarella
Date: Tue Jun 27 2023 - 03:50:18 EST
On Tue, Jun 27, 2023 at 07:39:41AM +0300, Arseniy Krasnov wrote:
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.
Okay, makes sense ;-)
Thanks,
Stefano
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