Re: [PATCH] virtio: make udp more efficient by avoiding indirect desc

[Qin Chuanyu <qinchuanyu@huawei.com>]

On 2014/2/11 23:43, Michael S. Tsirkin wrote:
> On Tue, Feb 11, 2014 at 10:58:52PM +0800, Qin Chuanyu wrote:
>> udp packet use 2 buffers at least, one for vnet_hdr and
>> one for skb->data.
>
> Not really, we use 1 buffer now with vnet_hdr inline with data.
>
I have found that there are related patch in Qemu,
Is there patch suit for vhost_net right now,
Or should I implement it myself ?

>> we could change the threshold from 2 to 3, so the udp packet
>> which data buff only using single desc will gain from this.
>> the guest would avoid from allocating memory dynamically.
>> the host would avoid from translating indirect desc.
>>
>> Signed-off-by: Chuanyu Qin <qinchuanyu@huawei.com>
>
> Optimization patch without any performance data?
> Such a change would need much more testing than that:
> would have to try various workloads with -net and -blk at least.
>
>> ---
>>   drivers/virtio/virtio_ring.c |    2 +-
>>   1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>> index 28b5338..88d008f 100644
>> --- a/drivers/virtio/virtio_ring.c
>> +++ b/drivers/virtio/virtio_ring.c
>> @@ -220,7 +220,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
>>
>>   	/* If the host supports indirect descriptor tables, and we have multiple
>>   	 * buffers, then go indirect. FIXME: tune this threshold */
>> -	if (vq->indirect && total_sg > 1 && vq->vq.num_free) {
>> +	if (vq->indirect && total_sg > 2 && vq->vq.num_free) {
>>   		head = vring_add_indirect(vq, sgs, next, total_sg, total_out,
>>   					  total_in,
>>   					  out_sgs, in_sgs, gfp);
>> --
>> 1.7.3.1.msysgit.0
>
>