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Message-ID: <5C135EB8.1000208@huawei.com>
Date: Fri, 14 Dec 2018 15:41:44 +0800
From: jiangyiwen <jiangyiwen@...wei.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
CC: Stefan Hajnoczi <stefanha@...hat.com>,
Jason Wang <jasowang@...hat.com>, <netdev@...r.kernel.org>,
<kvm@...r.kernel.org>, <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH v2 2/5] VSOCK: support fill data to mergeable rx buffer in
host
On 2018/12/13 22:48, Michael S. Tsirkin wrote:
> On Thu, Dec 13, 2018 at 11:08:04AM +0800, jiangyiwen wrote:
>> On 2018/12/12 23:37, Michael S. Tsirkin wrote:
>>> On Wed, Dec 12, 2018 at 05:29:31PM +0800, jiangyiwen wrote:
>>>> When vhost support VIRTIO_VSOCK_F_MRG_RXBUF feature,
>>>> it will merge big packet into rx vq.
>>>>
>>>> Signed-off-by: Yiwen Jiang <jiangyiwen@...wei.com>
>>>
>>> I feel this approach jumps into making interface changes for
>>> optimizations too quickly. For example, what prevents us
>>> from taking a big buffer, prepending each chunk
>>> with the header and writing it out without
>>> host/guest interface changes?
>>>
>>> This should allow optimizations such as vhost_add_used_n
>>> batching.
>>>
>>> I realize a header in each packet does have a cost,
>>> but it also has advantages such as improved robustness,
>>> I'd like to see more of an apples to apples comparison
>>> of the performance gain from skipping them.
>>>
>>>
>>
>> Hi Michael,
>>
>> I don't fully understand what you mean, do you want to
>> see a performance comparison that before performance and
>> only use batching?
>>
>> In my opinion, guest don't fill big buffer in rx vq because
>> the balance performance and guest memory pressure, add
>> mergeable feature can improve big packets performance,
>> as for small packets, I try to find out the reason, may be
>> the fluctuation of test results, or in mergeable mode, when
>> Host send a 4k packet to Guest, we should call vhost_get_vq_desc()
>> twice in host(hdr + 4k data), and in guest we also should call
>> virtqueue_get_buf() twice.
>>
>> Thanks,
>> Yiwen.
>
> What I mean is that at least some of the gain here is because
> larger skbs are passed up the stack.
>
Yes, the main gain is from larger skbs.
> You do not need larger packets to build larger skbs though.
> Just check that the addresses match and you can combine
> multiple fragments in a single skb.
>
>
I understand what you mean, if use batching send that the
performance also can be improved, I can test the real
performance result only use batching.
Thanks,
Yiwen.
>
>>>> ---
>>>> drivers/vhost/vsock.c | 111 ++++++++++++++++++++++++++++++--------
>>>> include/linux/virtio_vsock.h | 1 +
>>>> include/uapi/linux/virtio_vsock.h | 5 ++
>>>> 3 files changed, 94 insertions(+), 23 deletions(-)
>>>>
>>>> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>>>> index 34bc3ab..dc52b0f 100644
>>>> --- a/drivers/vhost/vsock.c
>>>> +++ b/drivers/vhost/vsock.c
>>>> @@ -22,7 +22,8 @@
>>>> #define VHOST_VSOCK_DEFAULT_HOST_CID 2
>>>>
>>>> enum {
>>>> - VHOST_VSOCK_FEATURES = VHOST_FEATURES,
>>>> + VHOST_VSOCK_FEATURES = VHOST_FEATURES |
>>>> + (1ULL << VIRTIO_VSOCK_F_MRG_RXBUF),
>>>> };
>>>>
>>>> /* Used to track all the vhost_vsock instances on the system. */
>>>> @@ -80,6 +81,69 @@ static struct vhost_vsock *vhost_vsock_get(u32 guest_cid)
>>>> return vsock;
>>>> }
>>>>
>>>> +/* This segment of codes are copied from drivers/vhost/net.c */
>>>> +static int get_rx_bufs(struct vhost_virtqueue *vq,
>>>> + struct vring_used_elem *heads, int datalen,
>>>> + unsigned *iovcount, unsigned int quota)
>>>> +{
>>>> + unsigned int out, in;
>>>> + int seg = 0;
>>>> + int headcount = 0;
>>>> + unsigned d;
>>>> + int ret;
>>>> + /*
>>>> + * len is always initialized before use since we are always called with
>>>> + * datalen > 0.
>>>> + */
>>>> + u32 uninitialized_var(len);
>>>> +
>>>> + while (datalen > 0 && headcount < quota) {
>>>> + if (unlikely(seg >= UIO_MAXIOV)) {
>>>> + ret = -ENOBUFS;
>>>> + goto err;
>>>> + }
>>>> +
>>>> + ret = vhost_get_vq_desc(vq, vq->iov + seg,
>>>> + ARRAY_SIZE(vq->iov) - seg, &out,
>>>> + &in, NULL, NULL);
>>>> + if (unlikely(ret < 0))
>>>> + goto err;
>>>> +
>>>> + d = ret;
>>>> + if (d == vq->num) {
>>>> + ret = 0;
>>>> + goto err;
>>>> + }
>>>> +
>>>> + if (unlikely(out || in <= 0)) {
>>>> + vq_err(vq, "unexpected descriptor format for RX: "
>>>> + "out %d, in %d\n", out, in);
>>>> + ret = -EINVAL;
>>>> + goto err;
>>>> + }
>>>> +
>>>> + heads[headcount].id = cpu_to_vhost32(vq, d);
>>>> + len = iov_length(vq->iov + seg, in);
>>>> + heads[headcount].len = cpu_to_vhost32(vq, len);
>>>> + datalen -= len;
>>>> + ++headcount;
>>>> + seg += in;
>>>> + }
>>>> +
>>>> + heads[headcount - 1].len = cpu_to_vhost32(vq, len + datalen);
>>>> + *iovcount = seg;
>>>> +
>>>> + /* Detect overrun */
>>>> + if (unlikely(datalen > 0)) {
>>>> + ret = UIO_MAXIOV + 1;
>>>> + goto err;
>>>> + }
>>>> + return headcount;
>>>> +err:
>>>> + vhost_discard_vq_desc(vq, headcount);
>>>> + return ret;
>>>> +}
>>>> +
>>>> static void
>>>> vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
>>>> struct vhost_virtqueue *vq)
>>>> @@ -87,22 +151,34 @@ static struct vhost_vsock *vhost_vsock_get(u32 guest_cid)
>>>> struct vhost_virtqueue *tx_vq = &vsock->vqs[VSOCK_VQ_TX];
>>>> bool added = false;
>>>> bool restart_tx = false;
>>>> + int mergeable;
>>>> + size_t vsock_hlen;
>>>>
>>>> mutex_lock(&vq->mutex);
>>>>
>>>> if (!vq->private_data)
>>>> goto out;
>>>>
>>>> + mergeable = vhost_has_feature(vq, VIRTIO_VSOCK_F_MRG_RXBUF);
>>>> + /*
>>>> + * Guest fill page for rx vq in mergeable case, so it will not
>>>> + * allocate pkt structure, we should reserve size of pkt in advance.
>>>> + */
>>>> + if (likely(mergeable))
>>>> + vsock_hlen = sizeof(struct virtio_vsock_pkt);
>>>> + else
>>>> + vsock_hlen = sizeof(struct virtio_vsock_hdr);
>>>> +
>>>> /* Avoid further vmexits, we're already processing the virtqueue */
>>>> vhost_disable_notify(&vsock->dev, vq);
>>>>
>>>> for (;;) {
>>>> struct virtio_vsock_pkt *pkt;
>>>> struct iov_iter iov_iter;
>>>> - unsigned out, in;
>>>> + unsigned out = 0, in = 0;
>>>> size_t nbytes;
>>>> size_t len;
>>>> - int head;
>>>> + s16 headcount;
>>>>
>>>> spin_lock_bh(&vsock->send_pkt_list_lock);
>>>> if (list_empty(&vsock->send_pkt_list)) {
>>>> @@ -116,16 +192,9 @@ static struct vhost_vsock *vhost_vsock_get(u32 guest_cid)
>>>> list_del_init(&pkt->list);
>>>> spin_unlock_bh(&vsock->send_pkt_list_lock);
>>>>
>>>> - head = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov),
>>>> - &out, &in, NULL, NULL);
>>>> - if (head < 0) {
>>>> - spin_lock_bh(&vsock->send_pkt_list_lock);
>>>> - list_add(&pkt->list, &vsock->send_pkt_list);
>>>> - spin_unlock_bh(&vsock->send_pkt_list_lock);
>>>> - break;
>>>> - }
>>>> -
>>>> - if (head == vq->num) {
>>>> + headcount = get_rx_bufs(vq, vq->heads, vsock_hlen + pkt->len,
>>>> + &in, likely(mergeable) ? UIO_MAXIOV : 1);
>>>> + if (headcount <= 0) {
>>>> spin_lock_bh(&vsock->send_pkt_list_lock);
>>>> list_add(&pkt->list, &vsock->send_pkt_list);
>>>> spin_unlock_bh(&vsock->send_pkt_list_lock);
>>>> @@ -133,24 +202,20 @@ static struct vhost_vsock *vhost_vsock_get(u32 guest_cid)
>>>> /* We cannot finish yet if more buffers snuck in while
>>>> * re-enabling notify.
>>>> */
>>>> - if (unlikely(vhost_enable_notify(&vsock->dev, vq))) {
>>>> + if (!headcount && unlikely(vhost_enable_notify(&vsock->dev, vq))) {
>>>> vhost_disable_notify(&vsock->dev, vq);
>>>> continue;
>>>> }
>>>> break;
>>>> }
>>>>
>>>> - if (out) {
>>>> - virtio_transport_free_pkt(pkt);
>>>> - vq_err(vq, "Expected 0 output buffers, got %u\n", out);
>>>> - break;
>>>> - }
>>>> -
>>>> len = iov_length(&vq->iov[out], in);
>>>> iov_iter_init(&iov_iter, READ, &vq->iov[out], in, len);
>>>>
>>>> - nbytes = copy_to_iter(&pkt->hdr, sizeof(pkt->hdr), &iov_iter);
>>>> - if (nbytes != sizeof(pkt->hdr)) {
>>>> + if (likely(mergeable))
>>>> + pkt->mrg_rxbuf_hdr.num_buffers = cpu_to_le16(headcount);
>>>> + nbytes = copy_to_iter(&pkt->hdr, vsock_hlen, &iov_iter);
>>>> + if (nbytes != vsock_hlen) {
>>>> virtio_transport_free_pkt(pkt);
>>>> vq_err(vq, "Faulted on copying pkt hdr\n");
>>>> break;
>>>> @@ -163,7 +228,7 @@ static struct vhost_vsock *vhost_vsock_get(u32 guest_cid)
>>>> break;
>>>> }
>>>>
>>>> - vhost_add_used(vq, head, sizeof(pkt->hdr) + pkt->len);
>>>> + vhost_add_used_n(vq, vq->heads, headcount);
>>>> added = true;
>>>>
>>>> if (pkt->reply) {
>>>> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>>>> index bf84418..da9e1fe 100644
>>>> --- a/include/linux/virtio_vsock.h
>>>> +++ b/include/linux/virtio_vsock.h
>>>> @@ -50,6 +50,7 @@ struct virtio_vsock_sock {
>>>>
>>>> struct virtio_vsock_pkt {
>>>> struct virtio_vsock_hdr hdr;
>>>> + struct virtio_vsock_mrg_rxbuf_hdr mrg_rxbuf_hdr;
>>>> struct work_struct work;
>>>> struct list_head list;
>>>> /* socket refcnt not held, only use for cancellation */
>>>> diff --git a/include/uapi/linux/virtio_vsock.h b/include/uapi/linux/virtio_vsock.h
>>>> index 1d57ed3..2292f30 100644
>>>> --- a/include/uapi/linux/virtio_vsock.h
>>>> +++ b/include/uapi/linux/virtio_vsock.h
>>>> @@ -63,6 +63,11 @@ struct virtio_vsock_hdr {
>>>> __le32 fwd_cnt;
>>>> } __attribute__((packed));
>>>>
>>>> +/* It add mergeable rx buffers feature */
>>>> +struct virtio_vsock_mrg_rxbuf_hdr {
>>>> + __le16 num_buffers; /* number of mergeable rx buffers */
>>>> +} __attribute__((packed));
>>>> +
>>>> enum virtio_vsock_type {
>>>> VIRTIO_VSOCK_TYPE_STREAM = 1,
>>>> };
>>>> --
>>>> 1.8.3.1
>>>>
>>>
>>> .
>>>
>>
>
> .
>
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