[dpdk-dev] [PATCH 4/4] net/virtio: improve offload check performance

Maxime Coquelin maxime.coquelin at redhat.com
Tue Jun 5 11:43:11 CEST 2018



On 06/05/2018 05:10 AM, Tiwei Bie wrote:
> On Mon, Jun 04, 2018 at 04:29:56PM +0200, Maxime Coquelin wrote:
>> On 06/04/2018 01:55 PM, Tiwei Bie wrote:
>>> On Fri, Jun 01, 2018 at 02:47:58PM +0200, Maxime Coquelin wrote:
> [...]
>>>> @@ -253,13 +246,15 @@ virtqueue_enqueue_xmit(struct virtnet_tx *txvq, struct rte_mbuf *cookie,
>>>>    	struct virtio_net_hdr *hdr;
>>>>    	int offload;
>>>> -	offload = tx_offload_enabled(vq->hw);
>>>>    	head_idx = vq->vq_desc_head_idx;
>>>>    	idx = head_idx;
>>>>    	dxp = &vq->vq_descx[idx];
>>>>    	dxp->cookie = (void *)cookie;
>>>>    	dxp->ndescs = needed;
>>>> +	offload = vq->hw->has_tx_offload &&
>>>> +		(cookie->ol_flags & PKT_TX_OFFLOAD_MASK);
>>>
>>> If features aren't negotiated, I think there is no need to
>>> check ol_flags and update the net header.
>>
>> Isn't what the code is doing?
>> has_tx_offload will be false if none of the Tx offload features have
>> been negotiated, so ol_flags won't be checked in that case.
> 
> Hmm.. Somehow I treated 'and' as 'or'..
> 
> I have another question. When 'can_push' is false
> and 'vq->hw->has_tx_offload' is true, there will
> be a chance that virtio net hdr won't be zeroed
> when ol_flags doesn't specify any Tx offloads.

Right, good catch.
It may be better to remove this small optimization.
Indeed, with the series, if the application does not enable offloads,
then the Virtio features are re-negotiated with the offload features.

Thanks,
Maxime

> Best regards,
> Tiwei Bie
> 


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