linux-kernel - Re: [RFC PATCH net-next 04/12] vhost

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Date:   Tue, 22 May 2018 20:39:49 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Jesse Brandeburg <jesse.brandeburg@...el.com>
Cc:     mst@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH net-next 04/12] vhost_net: split out datacopy logic



On 2018年05月22日 00:46, Jesse Brandeburg wrote:
> On Mon, 21 May 2018 17:04:25 +0800 Jason wrote:
>> Instead of mixing zerocopy and datacopy logics, this patch tries to
>> split datacopy logic out. This results for a more compact code and
>> specific optimization could be done on top more easily.
>>
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>> ---
>>   drivers/vhost/net.c | 111 +++++++++++++++++++++++++++++++++++++++++++++++-----
>>   1 file changed, 102 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
>> index 4ebac76..4682fcc 100644
>> --- a/drivers/vhost/net.c
>> +++ b/drivers/vhost/net.c
>> @@ -492,9 +492,95 @@ static bool vhost_has_more_pkts(struct vhost_net *net,
>>   	       likely(!vhost_exceeds_maxpend(net));
>>   }
>>   
>> +static void handle_tx_copy(struct vhost_net *net)
>> +{
>> +	struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
>> +	struct vhost_virtqueue *vq = &nvq->vq;
>> +	unsigned out, in;
> move "out" and "in" down to inside the for loop as well.
>
>> +	int head;
> move this "head" declaration inside for-loop below.

Will do these in next version, basically this function were just copied 
from handle_tx_zerocopy and remove unnecessary parts. So I'm thinking an 
independent patch from the beginning to avoid changes in two places.
>
>> +	struct msghdr msg = {
>> +		.msg_name = NULL,
>> +		.msg_namelen = 0,
>> +		.msg_control = NULL,
>> +		.msg_controllen = 0,
>> +		.msg_flags = MSG_DONTWAIT,
>> +	};
>> +	size_t len, total_len = 0;
>> +	int err;
>> +	size_t hdr_size;
>> +	struct socket *sock;
>> +	struct vhost_net_ubuf_ref *uninitialized_var(ubufs);
>> +	int sent_pkts = 0;
> why do we need so many locals?

So it looks to me ubufs is unnecessary but all other is really needed.

>
>> +
>> +	mutex_lock(&vq->mutex);
>> +	sock = vq->private_data;
>> +	if (!sock)
>> +		goto out;
>> +
>> +	if (!vq_iotlb_prefetch(vq))
>> +		goto out;
>> +
>> +	vhost_disable_notify(&net->dev, vq);
>> +	vhost_net_disable_vq(net, vq);
>> +
>> +	hdr_size = nvq->vhost_hlen;
>> +
>> +	for (;;) {
>> +		head = vhost_net_tx_get_vq_desc(net, vq, vq->iov,
>> +						ARRAY_SIZE(vq->iov),
>> +						&out, &in);
>> +		/* On error, stop handling until the next kick. */
>> +		if (unlikely(head < 0))
>> +			break;
>> +		/* Nothing new?  Wait for eventfd to tell us they refilled. */
>> +		if (head == vq->num) {
>> +			if (unlikely(vhost_enable_notify(&net->dev, vq))) {
>> +				vhost_disable_notify(&net->dev, vq);
>> +				continue;
>> +			}
>> +			break;
>> +		}
>> +		if (in) {
>> +			vq_err(vq, "Unexpected descriptor format for TX: "
>> +			       "out %d, int %d\n", out, in);
> don't break strings, keep all the bits between " " together, even if it
> is longer than 80 chars.

Ok.

>
>> +			break;
>> +		}
>> +
>> +		len = init_iov_iter(vq, &msg.msg_iter, hdr_size, out);
>> +		if (len < 0)
>> +			break;
> same comment as previous patch, len is a size_t which is unsigned.

Yes.

>
>> +
>> +		total_len += len;
>> +		if (total_len < VHOST_NET_WEIGHT &&
>> +		    vhost_has_more_pkts(net, vq)) {
>> +			msg.msg_flags |= MSG_MORE;
>> +		} else {
>> +			msg.msg_flags &= ~MSG_MORE;
>> +		}
> don't need { } here.

Right.

>> +
>> +		/* TODO: Check specific error and bomb out unless ENOBUFS? */
>> +		err = sock->ops->sendmsg(sock, &msg, len);
>> +		if (unlikely(err < 0)) {
>> +			vhost_discard_vq_desc(vq, 1);
>> +			vhost_net_enable_vq(net, vq);
>> +			break;
>> +		}
>> +		if (err != len)
>> +			pr_debug("Truncated TX packet: "
>> +				 " len %d != %zd\n", err, len);
> single line " " string please
>

Will fix.

Thanks