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

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Message-ID: <1901174467.9092625.1661483462548.JavaMail.zimbra@sjtu.edu.cn>
Date:   Fri, 26 Aug 2022 11:11:02 +0800 (CST)
From:   Guo Zhi <qtxuning1999@...u.edu.cn>
To:     jasowang <jasowang@...hat.com>
Cc:     eperezma <eperezma@...hat.com>, sgarzare <sgarzare@...hat.com>,
        Michael Tsirkin <mst@...hat.com>,
        netdev <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        virtualization <virtualization@...ts.linux-foundation.org>
Subject: Re: [RFC v2 3/7] vsock: batch buffers in tx



----- Original Message -----
> From: "jasowang" <jasowang@...hat.com>
> To: "Guo Zhi" <qtxuning1999@...u.edu.cn>, "eperezma" <eperezma@...hat.com>, "sgarzare" <sgarzare@...hat.com>, "Michael
> Tsirkin" <mst@...hat.com>
> Cc: "netdev" <netdev@...r.kernel.org>, "linux-kernel" <linux-kernel@...r.kernel.org>, "kvm list" <kvm@...r.kernel.org>,
> "virtualization" <virtualization@...ts.linux-foundation.org>
> Sent: Thursday, August 25, 2022 3:08:58 PM
> Subject: Re: [RFC v2 3/7] vsock: batch buffers in tx

> 在 2022/8/17 21:57, Guo Zhi 写道:
>> 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@...u.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);
> 
> 
> I may miss something but spec said "The device then skips forward in the
> ring according to the size of the batch. ".
> 
> I don't see how it is done here.
> 
> Thanks
> 

It can skip them in __vhost_add_used_n if _F_IN_ORDER is negotiated.
last_used_idx will be added by size of the batch.

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