Re: [RFC v2 3/7] vsock: batch buffers in tx

[Guo Zhi <qtxuning1999@sjtu.edu.cn>]

----- Original Message -----
> From: "eperezma" <eperezma@redhat.com>
> To: "Guo Zhi" <qtxuning1999@sjtu.edu.cn>
> Cc: "jasowang" <jasowang@redhat.com>, "sgarzare" <sgarzare@redhat.com>, "Michael Tsirkin" <mst@redhat.com>, "netdev"
> <netdev@vger.kernel.org>, "linux-kernel" <linux-kernel@vger.kernel.org>, "kvm list" <kvm@vger.kernel.org>,
> "virtualization" <virtualization@lists.linux-foundation.org>
> Sent: Thursday, August 18, 2022 2:19:29 PM
> Subject: Re: [RFC v2 3/7] vsock: batch buffers in tx

> On Wed, Aug 17, 2022 at 3:58 PM Guo Zhi <qtxuning1999@sjtu.edu.cn> wrote:
>>
>> Vsock uses buffers in order, and for tx driver doesn't have to
>> know the length of the buffer. So we can do a batch for vsock if
>> in order negotiated, only write one used ring for a batch of buffers
>>
>> Signed-off-by: Guo Zhi <qtxuning1999@sjtu.edu.cn>
>> ---
>>  drivers/vhost/vsock.c | 9 ++++++++-
>>  1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>> index 368330417bde..b0108009c39a 100644
>> --- a/drivers/vhost/vsock.c
>> +++ b/drivers/vhost/vsock.c
>> @@ -500,6 +500,7 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work
>> *work)
>>         int head, pkts = 0, total_len = 0;
>>         unsigned int out, in;
>>         bool added = false;
>> +       int last_head = -1;
>>
>>         mutex_lock(&vq->mutex);
>>
>> @@ -551,10 +552,16 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work
>> *work)
>>                 else
>>                         virtio_transport_free_pkt(pkt);
>>
>> -               vhost_add_used(vq, head, 0);
>> +               if (!vhost_has_feature(vq, VIRTIO_F_IN_ORDER))
>> +                       vhost_add_used(vq, head, 0);
>> +               else
>> +                       last_head = head;
>>                 added = true;
>>         } while(likely(!vhost_exceeds_weight(vq, ++pkts, total_len)));
>>
>> +       /* If in order feature negotiaged, we can do a batch to increase
>> performance */
>> +       if (vhost_has_feature(vq, VIRTIO_F_IN_ORDER) && last_head != -1)
>> +               vhost_add_used(vq, last_head, 0);
> 
> Expanding my previous mail on patch 1, you can also use this in vsock
> tx queue code. This way, no modifications to vhost.c functions are
> needed.
> 
> Thanks!

As replied in patch 1, no modification to vhost is not feasible.

Thanks!

> 
>>  no_more_replies:
>>         if (added)
>>                 vhost_signal(&vsock->dev, vq);
>> --
>> 2.17.1
>>