* Re: [PATCH net-next v2 2/4] vsock/virtio: support to send non-linear skb
[not found] ` <1ac4be11-0814-05af-6c2e-8563ac15e206@sberdevices.ru>
@ 2023-07-19 7:36 ` Stefano Garzarella
0 siblings, 0 replies; 2+ messages in thread
From: Stefano Garzarella @ 2023-07-19 7:36 UTC (permalink / raw)
To: Arseniy Krasnov
Cc: Bobby Eshleman, kvm, Michael S. Tsirkin, netdev, linux-kernel,
virtualization, oxffffaa, Eric Dumazet, Stefan Hajnoczi, kernel,
Jakub Kicinski, Paolo Abeni, David S. Miller
On Wed, Jul 19, 2023 at 07:46:05AM +0300, Arseniy Krasnov wrote:
>
>
>On 18.07.2023 23:27, Michael S. Tsirkin wrote:
>> On Tue, Jul 18, 2023 at 09:02:35PM +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@sberdevices.ru>
>>> Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
>>> ---
>>> net/vmw_vsock/virtio_transport.c | 40 +++++++++++++++++++++++++++-----
>>> 1 file changed, 34 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>>> index e95df847176b..6cbb45bb12d2 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 +113,38 @@ 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[out_sg], virtio_vsock_hdr(skb),
>>> + sizeof(*virtio_vsock_hdr(skb)));
>>> + sgs[out_sg] = &bufs[out_sg];
>>> + out_sg++;
>>> +
>>> + if (!skb_is_nonlinear(skb)) {
>>> + if (skb->len > 0) {
>>> + sg_init_one(&bufs[out_sg], skb->data, skb->len);
>>> + sgs[out_sg] = &bufs[out_sg];
>>> + out_sg++;
>>> + }
>>> + } else {
>>> + 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);
>>>
>>> - 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;
>>> + /* We will use 'page_to_virt()' for userspace page here,
>>
>> don't put comments after code they refer to, please?
>>
>>> + * because virtio layer will call 'virt_to_phys()' later
>>
>> it will but not always. sometimes it's the dma mapping layer.
>>
>>
>>> + * to fill buffer descriptor. We don't touch memory at
>>> + * "virtual" address of this page.
>>
>>
>> you need to stick "the" in a bunch of places above.
>
>Ok, I'll fix this comment!
>
>>
>>> + */
>>> + sg_init_one(&bufs[out_sg],
>>> + va + skb_frag->bv_offset,
>>> + skb_frag->bv_len);
>>> + sgs[out_sg] = &bufs[out_sg];
>>> + out_sg++;
>>> + }
>>> }
>>>
>>> ret = virtqueue_add_sgs(vq, sgs, out_sg, in_sg, skb, GFP_KERNEL);
>>
>>
>> There's a problem here: if there vq is small this will fail.
>> So you really should check free vq s/gs and switch to non-zcopy
>> if too small.
>
>Ok, so idea is that:
>
>if (out_sg > vq->num_free)
> reorganise current skb for copy mode (e.g. 2 out_sg - header and data)
> and try to add it to vq again.
>
>?
>
>@Stefano, I'll remove net-next tag (guess RFC is not required again, but not net-next
>anyway) as this change will require review. R-b I think should be also removed. All
>other patches in this set still unchanged.
It's still a new feature so we have net-next tree as the target, right?
I think we should keep net-next. Even if patches require to be
re-reviewed, net-next indicates the tree where we want these to be merge
and for new features is the right one.
Ack for not putting RFC again and for R-b removal for this patch.
Thanks,
Stefano
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