Re: [dpdk-dev] [PATCH] net/virtio: fix indirect descriptors reconnection

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 9/23/21 11:21, Ding, Xuan wrote:
> Hi Maxime,
> 
>> -----Original Message-----
>> From: Ding, Xuan
>> Sent: Thursday, September 23, 2021 4:36 PM
>> To: Maxime Coquelin <maxime.coquelin@redhat.com>; Xia, Chenbo
>> <Chenbo.Xia@intel.com>
>> Cc: dev@dpdk.org; Hu, Jiayu <Jiayu.Hu@intel.com>; Wang, Yinan
>> <yinan.wang@intel.com>; stable@dpdk.org; Liu, Yong <yong.liu@intel.com>
>> Subject: RE: [PATCH] net/virtio: fix indirect descriptors reconnection
>>
>> Hi Maxime,
>>
>>> -----Original Message-----
>>> From: Maxime Coquelin <maxime.coquelin@redhat.com>
>>> Sent: Thursday, September 23, 2021 4:16 PM
>>> To: Ding, Xuan <xuan.ding@intel.com>; Xia, Chenbo <chenbo.xia@intel.com>
>>> Cc: dev@dpdk.org; Hu, Jiayu <jiayu.hu@intel.com>; Wang, Yinan
>>> <yinan.wang@intel.com>; stable@dpdk.org; Liu, Yong <yong.liu@intel.com>
>>> Subject: Re: [PATCH] net/virtio: fix indirect descriptors reconnection
>>>
>>> Hi Xuan,
>>>
>>> On 8/19/21 07:35, Xuan Ding wrote:
>>>> Since packed indirect descriptors are added and initialized when
>>>> initializing vring, the reconnection path also needs to be considered.
>>>>
>>>> Fixes: 381f39ebb78a ("net/virtio: fix packed ring indirect descricptors setup")
>>>> Cc: stable@dpdk.org
>>>> Cc: yong.liu@intel.com
>>>>
>>>> Signed-off-by: Xuan Ding <xuan.ding@intel.com>
>>>> ---
>>>>    drivers/net/virtio/virtqueue.c | 14 ++++++++++++++
>>>>    1 file changed, 14 insertions(+)
>>>>
>>>> diff --git a/drivers/net/virtio/virtqueue.c b/drivers/net/virtio/virtqueue.c
>>>> index 1f9af3c31b..47229f35c4 100644
>>>> --- a/drivers/net/virtio/virtqueue.c
>>>> +++ b/drivers/net/virtio/virtqueue.c
>>>> @@ -208,6 +208,20 @@ virtqueue_txvq_reset_packed(struct virtqueue *vq)
>>>>    			rte_pktmbuf_free(dxp->cookie);
>>>>    			dxp->cookie = NULL;
>>>>    		}
>>>
>>> It makes me think we might save quite some bytes by not allocating
>>> indirect descriptors when feature is not negotiated, but it might have
>>> a cost in term of performance.
>>
>> Do you mean we allocate the indirect descriptors after checking the indirect
>> feature in virtio TX queue,
>> instead of allocating it at initialization?
>> If so, that makes sense, and hence we don't to initialize it in two places.
> 
> Sorry for replying myself, as for performance, I can have a try and test the
> impact on performance.

Thanks for looking at this, but maybe that could be done later, after
having the fix merged first if you don't have the bandwidth?

Maxime
> Thanks,
> Xuan
> 
>>
>>>
>>>> +
>>>> +		struct virtio_tx_region *txr;
>>>
>>> Don't mix declarations within code.
>>>
>>>> +		txr = txvq->virtio_net_hdr_mz->addr;
>>>> +		/* first indirect descriptor is always the tx header */
>>>> +		struct vring_packed_desc *start_dp =
>>>> +			txr[desc_idx].tx_packed_indir;
>>>
>>> Ditto.
>>
>> Thanks, will update in next version.
>>
>> Regards,
>> Xuan
>>
>>>
>>>> +		vring_desc_init_indirect_packed(start_dp,
>>>> +		      RTE_DIM(txr[desc_idx].tx_packed_indir));
>>>> +		start_dp->addr = txvq->virtio_net_hdr_mem
>>>> +			+ desc_idx * sizeof(*txr)
>>>> +			+ offsetof(struct virtio_tx_region,
>>>> +				   tx_hdr);
>>>> +		start_dp->len = vq->hw->vtnet_hdr_size;
>>>> +
>>>>    	}
>>>>
>>>>    	vring_desc_init_packed(vq, size);
>>>>
>>>
>>> Thanks,
>>> Maxime
>