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To: "Liu, Yong" <yong.liu@intel.com>, "Bie, Tiwei" <tiwei.bie@intel.com>
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From: Maxime Coquelin <maxime.coquelin@redhat.com>
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Subject: Re: [dpdk-dev] [PATCH v3 08/11] net/virtio: add in-order Rx/Tx into
	selection
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On 06/28/2018 05:39 PM, Liu, Yong wrote:
> 
> 
>> -----Original Message-----
>> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
>> Sent: Thursday, June 28, 2018 11:16 PM
>> To: Liu, Yong <yong.liu@intel.com>; Bie, Tiwei <tiwei.bie@intel.com>
>> Cc: Wang, Zhihong <zhihong.wang@intel.com>; dev@dpdk.org
>> Subject: Re: [PATCH v3 08/11] net/virtio: add in-order Rx/Tx into
>> selection
>>
>>
>>
>> On 06/28/2018 11:52 PM, Marvin Liu wrote:
>>> After IN_ORDER Rx/Tx paths added, need to update Rx/Tx path selection
>>> logic.
>>>
>>> Rx path select logic: If IN_ORDER is disabled will select normal Rx
>>> path. If IN_ORDER is enabled, Rx offload and merge-able are disabled
>>> will select simple Rx path. Otherwise will select IN_ORDER Rx path.
>>>
>>> Tx path select logic: If IN_ORDER is disabled will select normal Tx
>>> path. If IN_ORDER is enabled and merge-able is disabled will select
>>> simple Tx path. Otherwise will select IN_ORDER Tx path.
>>>
>>> Signed-off-by: Marvin Liu <yong.liu@intel.com>
>>>
>>> diff --git a/drivers/net/virtio/virtio_ethdev.c
>> b/drivers/net/virtio/virtio_ethdev.c
>>> index df50a571a..2b3d65f80 100644
>>> --- a/drivers/net/virtio/virtio_ethdev.c
>>> +++ b/drivers/net/virtio/virtio_ethdev.c
>>> @@ -1320,6 +1320,11 @@ set_rxtx_funcs(struct rte_eth_dev *eth_dev)
>>>    		PMD_INIT_LOG(INFO, "virtio: using simple Rx path on port %u",
>>>    			eth_dev->data->port_id);
>>>    		eth_dev->rx_pkt_burst = virtio_recv_pkts_vec;
>>> +	} else if (hw->use_inorder_rx) {
>>> +		PMD_INIT_LOG(INFO,
>>> +			"virtio: using inorder mergeable buffer Rx path on
>> port %u",
>>> +			eth_dev->data->port_id);
>>> +		eth_dev->rx_pkt_burst = &virtio_recv_mergeable_pkts_inorder;
>>>    	} else if (vtpci_with_feature(hw, VIRTIO_NET_F_MRG_RXBUF)) {
>>>    		PMD_INIT_LOG(INFO,
>>>    			"virtio: using mergeable buffer Rx path on port %u",
>>> @@ -1335,6 +1340,10 @@ set_rxtx_funcs(struct rte_eth_dev *eth_dev)
>>>    		PMD_INIT_LOG(INFO, "virtio: using simple Tx path on port %u",
>>>    			eth_dev->data->port_id);
>>>    		eth_dev->tx_pkt_burst = virtio_xmit_pkts_simple;
>>> +	} else if (hw->use_inorder_tx) {
>>> +		PMD_INIT_LOG(INFO, "virtio: using inorder Tx path on port %u",
>>> +			eth_dev->data->port_id);
>>> +		eth_dev->tx_pkt_burst = virtio_xmit_pkts_inorder;
>>>    	} else {
>>>    		PMD_INIT_LOG(INFO, "virtio: using standard Tx path on port %u",
>>>    			eth_dev->data->port_id);
>>> @@ -1871,24 +1880,24 @@ virtio_dev_configure(struct rte_eth_dev *dev)
>>>
>>>    	rte_spinlock_init(&hw->state_lock);
>>>
>>> -	hw->use_simple_rx = 1;
>>> -	hw->use_simple_tx = 1;
>>> -
>>>    #if defined RTE_ARCH_ARM64 || defined RTE_ARCH_ARM
>>>    	if (!rte_cpu_get_flag_enabled(RTE_CPUFLAG_NEON)) {
>>>    		hw->use_simple_rx = 0;
>>>    		hw->use_simple_tx = 0;
>>>    	}
>>>    #endif
>>> -	if (vtpci_with_feature(hw, VIRTIO_NET_F_MRG_RXBUF)) {
>>> -		hw->use_simple_rx = 0;
>>> -		hw->use_simple_tx = 0;
>>> +	if (vtpci_with_feature(hw, VIRTIO_F_IN_ORDER)) {
>>> +		if (vtpci_with_feature(hw, VIRTIO_NET_F_MRG_RXBUF)) {
>>> +			hw->use_inorder_rx = 1;
>>> +			hw->use_inorder_tx = 1;
>>> +		} else {
>>> +			hw->use_simple_tx = 1;
>>> +			if (!(rx_offloads & (DEV_RX_OFFLOAD_UDP_CKSUM |
>>> +					     DEV_RX_OFFLOAD_TCP_CKSUM)))
>>> +				hw->use_simple_rx = 1;
>>> +		}
>>
>> It seems to be wrong.
>> For example if IN_ORDER hasn't been negotiated, we might want to use the
>> simple path if no rx offload have been requested by the application.
>>
>> It was the case before the patch if I'm not mistaken.
> 
> Maxime,
> IN_ORDER is the prerequisite for selection simple rx/tx path. So when IN_ORDER + mergeable off + no rx offload will chose simple rx path.

Ok, I wonder in that case if I could just remove the simple Tx path in
my series as it is not compliant with IN_ORDER.
Tiwei, what's your take on this?

Also, I wonder if it would make sense to backport the vhost patch that 
advertize IN_ORDER features to the LTS, as no functional changes, except
that it prevents using "simple/inorder" path with dequeue zero copy,
which is a good thing.

Any thoughts?

>>
>> Also, with ARM platform, we force not to use simple path, but in case
>> IN_ORDER has been negotiated but not MRG_RXBUF, it gets re-enabled.
> 
> Will move ARM force action behind normal selection, thus can satisfy ARM.

I can change when applying.

Thanks,
Maxime

> Thanks,
> Marvin
> 
>>
>>>    	}
>>>
>>> -	if (rx_offloads & (DEV_RX_OFFLOAD_UDP_CKSUM |
>>> -			   DEV_RX_OFFLOAD_TCP_CKSUM))
>>> -		hw->use_simple_rx = 0;
>>> -
>>>    	return 0;
>>>    }
>>>
>>>