Re: [PATCH 1/5] VSOCK: support fill mergeable rx buffer in guest

[jiangyiwen <jiangyiwen@huawei.com>]

On 2018/11/6 11:38, Jason Wang wrote:
> 
> On 2018/11/5 下午3:45, jiangyiwen wrote:
>> In driver probing, if virtio has VIRTIO_VSOCK_F_MRG_RXBUF feature,
>> it will fill mergeable rx buffer, support for host send mergeable
>> rx buffer. It will fill a page everytime to compact with small
>> packet and big packet.
>>
>> Signed-off-by: Yiwen Jiang <jiangyiwen@huawei.com>
>> ---
>>   include/linux/virtio_vsock.h     |  3 ++
>>   net/vmw_vsock/virtio_transport.c | 72 +++++++++++++++++++++++++++++-----------
>>   2 files changed, 56 insertions(+), 19 deletions(-)
>>
>> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>> index e223e26..bf84418 100644
>> --- a/include/linux/virtio_vsock.h
>> +++ b/include/linux/virtio_vsock.h
>> @@ -14,6 +14,9 @@
>>   #define VIRTIO_VSOCK_MAX_BUF_SIZE        0xFFFFFFFFUL
>>   #define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE        (1024 * 64)
>>
>> +/* Virtio-vsock feature */
>> +#define VIRTIO_VSOCK_F_MRG_RXBUF 0 /* Host can merge receive buffers. */
>> +
>>   enum {
>>       VSOCK_VQ_RX     = 0, /* for host to guest data */
>>       VSOCK_VQ_TX     = 1, /* for guest to host data */
>> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>> index 5d3cce9..2040a9e 100644
>> --- a/net/vmw_vsock/virtio_transport.c
>> +++ b/net/vmw_vsock/virtio_transport.c
>> @@ -64,6 +64,7 @@ struct virtio_vsock {
>>       struct virtio_vsock_event event_list[8];
>>
>>       u32 guest_cid;
>> +    bool mergeable;
>>   };
>>
>>   static struct virtio_vsock *virtio_vsock_get(void)
>> @@ -256,6 +257,25 @@ static int virtio_transport_send_pkt_loopback(struct virtio_vsock *vsock,
>>       return 0;
>>   }
>>
>> +static int fill_mergeable_rx_buff(struct virtqueue *vq)
>> +{
>> +    void *page = NULL;
>> +    struct scatterlist sg;
>> +    int err;
>> +
>> +    page = (void *)get_zeroed_page(GFP_KERNEL);
> 
> 
> Any reason to use zeroed page?

In previous version, the entire structure of virtio_vsock_pkt is preallocated
in guest use kzalloc, it is a contiguous zeroed physical memory, but host only
need to fill virtio_vsock_hdr size.

However, in mergeable rx buffer version, we only fill a page in vring descriptor
in guest, and I will reserve size of virtio_vsock_pkt in host instead of write
the total size of virtio_vsock_pkt, for the correctness of structure value,
we should set zeroed page in advance.

> 
> 
>> +    if (!page)
>> +        return -ENOMEM;
>> +
>> +    sg_init_one(&sg, page, PAGE_SIZE);
> 
> 
> FYI, for virtio-net we have several optimizations for mergeable rx buffer:
> 
> - skb_page_frag_refill() which can use high order page and reduce the stress of page allocator
> 

You're right, initially I want to use a memory poll to manage the rx buffer,
and then use this in the later optimized patch. Your advice is very great.

> - we don't use fixed buffer size, instead we use EWMA to estimate the possible rx buffer size to avoid internal fragmentation
> 

Ok, I analysis the feature and consider add it into my patches.

> 
> If we can try to reuse virtio-net driver, we will get those nice features.
> 

Yes, after all virtio-net has a very good ecological environment, and it also
do many performance optimization, it is actually a good idea.

> 
> Thanks
> 
> 
>> +
>> +    err = virtqueue_add_inbuf(vq, &sg, 1, page, GFP_KERNEL);
>> +    if (err < 0)
>> +        free_page((unsigned long) page);
>> +
>> +    return err;
>> +}
>> +
>>   static void virtio_vsock_rx_fill(struct virtio_vsock *vsock)
>>   {
>>       int buf_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE;
>> @@ -267,27 +287,33 @@ static void virtio_vsock_rx_fill(struct virtio_vsock *vsock)
>>       vq = vsock->vqs[VSOCK_VQ_RX];
>>
>>       do {
>> -        pkt = kzalloc(sizeof(*pkt), GFP_KERNEL);
>> -        if (!pkt)
>> -            break;
>> +        if (vsock->mergeable) {
>> +            ret = fill_mergeable_rx_buff(vq);
>> +            if (ret)
>> +                break;
>> +        } else {
>> +            pkt = kzalloc(sizeof(*pkt), GFP_KERNEL);
>> +            if (!pkt)
>> +                break;
>>
>> -        pkt->buf = kmalloc(buf_len, GFP_KERNEL);
>> -        if (!pkt->buf) {
>> -            virtio_transport_free_pkt(pkt);
>> -            break;
>> -        }
>> +            pkt->buf = kmalloc(buf_len, GFP_KERNEL);
>> +            if (!pkt->buf) {
>> +                virtio_transport_free_pkt(pkt);
>> +                break;
>> +            }
>>
>> -        pkt->len = buf_len;
>> +            pkt->len = buf_len;
>>
>> -        sg_init_one(&hdr, &pkt->hdr, sizeof(pkt->hdr));
>> -        sgs[0] = &hdr;
>> +            sg_init_one(&hdr, &pkt->hdr, sizeof(pkt->hdr));
>> +            sgs[0] = &hdr;
>>
>> -        sg_init_one(&buf, pkt->buf, buf_len);
>> -        sgs[1] = &buf;
>> -        ret = virtqueue_add_sgs(vq, sgs, 0, 2, pkt, GFP_KERNEL);
>> -        if (ret) {
>> -            virtio_transport_free_pkt(pkt);
>> -            break;
>> +            sg_init_one(&buf, pkt->buf, buf_len);
>> +            sgs[1] = &buf;
>> +            ret = virtqueue_add_sgs(vq, sgs, 0, 2, pkt, GFP_KERNEL);
>> +            if (ret) {
>> +                virtio_transport_free_pkt(pkt);
>> +                break;
>> +            }
>>           }
>>           vsock->rx_buf_nr++;
>>       } while (vq->num_free);
>> @@ -588,6 +614,9 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
>>       if (ret < 0)
>>           goto out_vqs;
>>
>> +    if (virtio_has_feature(vdev, VIRTIO_VSOCK_F_MRG_RXBUF))
>> +        vsock->mergeable = true;
>> +
>>       vsock->rx_buf_nr = 0;
>>       vsock->rx_buf_max_nr = 0;
>>       atomic_set(&vsock->queued_replies, 0);
>> @@ -640,8 +669,12 @@ static void virtio_vsock_remove(struct virtio_device *vdev)
>>       vdev->config->reset(vdev);
>>
>>       mutex_lock(&vsock->rx_lock);
>> -    while ((pkt = virtqueue_detach_unused_buf(vsock->vqs[VSOCK_VQ_RX])))
>> -        virtio_transport_free_pkt(pkt);
>> +    while ((pkt = virtqueue_detach_unused_buf(vsock->vqs[VSOCK_VQ_RX]))) {
>> +        if (vsock->mergeable)
>> +            free_page((unsigned long)(void *)pkt);
>> +        else
>> +            virtio_transport_free_pkt(pkt);
>> +    }
>>       mutex_unlock(&vsock->rx_lock);
>>
>>       mutex_lock(&vsock->tx_lock);
>> @@ -683,6 +716,7 @@ static void virtio_vsock_remove(struct virtio_device *vdev)
>>   };
>>
>>   static unsigned int features[] = {
>> +    VIRTIO_VSOCK_F_MRG_RXBUF,
>>   };
>>
>>   static struct virtio_driver virtio_vsock_driver = {
> 
> .
> 


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