Subject: Re: [PATCH V2 4/6] vhost_net: determine whether or not to use zerocopy at one time

From: Jason Wang <[email-masked]>
Date: Mon, 02 Sep 2013 11:15:14 +0800

On 08/31/2013 02:35 AM, Sergei Shtylyov wrote:
> Hello.
>
> On 08/30/2013 08:29 AM, Jason Wang wrote:
>
>> Currently, even if the packet length is smaller than
>> VHOST_GOODCOPY_LEN, if
>> upend_idx != done_idx we still set zcopy_used to true and rollback
>> this choice
>> later. This could be avoided by determine zerocopy once by checking all
>> conditions at one time before.
>
>> Signed-off-by: Jason Wang <[email-masked]>
>> ---
>>   drivers/vhost/net.c |   46
>> +++++++++++++++++++---------------------------
>>   1 files changed, 19 insertions(+), 27 deletions(-)
>
>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
>> index 8a6dd0d..ff60c2a 100644
>> --- a/drivers/vhost/net.c
>> +++ b/drivers/vhost/net.c
>> @@ -404,43 +404,35 @@ static void handle_tx(struct vhost_net *net)
>>                      iov_length(nvq->hdr, s), hdr_size);
>>               break;
>>           }
>> -        zcopy_used = zcopy && (len >= VHOST_GOODCOPY_LEN ||
>> -                       nvq->upend_idx != nvq->done_idx);
>> +
>> +        zcopy_used = zcopy && len >= VHOST_GOODCOPY_LEN
>> +            && (nvq->upend_idx + 1) % UIO_MAXIOV != nvq->done_idx
>> +            && vhost_net_tx_select_zcopy(net);
>
>    Could you leave && on a first of two lines, matching the previous
> style?
>

ok.
>>
>>           /* use msg_control to pass vhost zerocopy ubuf info to skb */
>>           if (zcopy_used) {
>> +            struct ubuf_info *ubuf;
>> +            ubuf = nvq->ubuf_info + nvq->upend_idx;
>> +
>>               vq->heads[nvq->upend_idx].id = head;
> [...]
>> +            vq->heads[nvq->upend_idx].len = VHOST_DMA_IN_PROGRESS;
>> +            ubuf->callback = vhost_zerocopy_callback;
>> +            ubuf->ctx = nvq->ubufs;
>> +            ubuf->desc = nvq->upend_idx;
>> +            msg.msg_control = ubuf;
>> +            msg.msg_controllen = sizeof(ubuf);
>
>    'sizeof(ubuf)' where 'ubuf' is a pointer? Are you sure it shouldn't
> be 'sizeof(*ubuf)'?

Yes, pointer is sufficiet. Vhost allocate an arrays of ubuf and
tun/macvtap just need a reference of it.
>
> WBR, Sergei
>
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