Re: [dpdk-dev] [PATCH v2] net/pcap: rx_iface_in stream type support

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 6/16/2018 10:27 AM, Ido Goshen wrote:
> Is pcap_sendpacket() to the same pcap_t handle thread-safe? I couldn't find clear answer so I'd rather assume not.
> If it's not thread-safe then supporting multiple "iface"'s will require multiple pcap_open_live()'s and we are back in the same place.

I am not suggesting extra multi thread safety.

Currently in "iface" path, following is hardcoded:
	pcaps.num_of_queue = 1;
	dumpers.num_of_queue = 1;

It can be possible to update that path to support multiple queue while using
"iface" devargs.

> 
>>> I am not sure exiting behavior is intentional, which is capturing sent packages in Rx pcap handler to same interface.
>>> Are you aware of any use case of existing behavior? Perhaps it can be option to set PCAP_D_IN by default for rx_iface argument.
> Even if unintentional I find it very useful for testing, as this way it's very easy to send traffic to the app by tcpreplay on the same host the app is running on. 
> Using tcpreplay is in the out direction that will not be captured if PCAP_D_IN is set. 
> If PCAP_D_IN is the only option then it will require external device (or some networking trick) to send packets to the app.
> So, I'd say it is good for testing but less good for real functionality 

OK to keep it if there is a usecase.

> 
> -----Original Message-----
> From: Ferruh Yigit <ferruh.yigit@intel.com> 
> Sent: Friday, June 15, 2018 3:53 PM
> To: Ido Goshen <Ido@cgstowernetworks.com>
> Cc: dev@dpdk.org
> Subject: Re: [PATCH v2] net/pcap: rx_iface_in stream type support
> 
> On 6/14/2018 9:44 PM, Ido Goshen wrote:
>> I think we are starting to mix two things One is how to configure pcap 
>> eth dev with multiple queues and I totally agree it would have been nicer to just say something like "max_tx_queues =N" instead of needing to write "tx_iface" N times, but as it was already supported in that way (for any reason?) I wasn't trying to enhance or change it.
>> The other issue is pcap direction API, which I was trying to expose to users of dpdk pcap device.
> 
> Hi Ido,
> 
> Assuming "iface" argument solves the direction issue, I am suggestion adding multiqueue support to "iface" argument as a solution to your problem.
> 
> I am not suggesting using new arguments like "max_tx_queues =N", "iface" can be used same as how rx/tx_ifcase used now, provide it multiple times.
> 
>> Refer to https://www.tcpdump.org/manpages/pcap_setdirection.3pcap.txt 
>> or man tcpdump for -P/--direction in|out|inout option, Actually I 
>> think a more realistic emulation of a physical device (non-virtual) 
>> would be to capture only the incoming direction (set PCAP_D_IN), again 
>> the existing behavior is very useful too and I didn't try to change or 
>> eliminate it but just add additional stream type option
> 
> I am not sure exiting behavior is intentional, which is capturing sent packages in Rx pcap handler to same interface.
> Are you aware of any use case of existing behavior? Perhaps it can be option to set PCAP_D_IN by default for rx_iface argument.
> 
>>
>> -----Original Message-----
>> From: Ferruh Yigit <ferruh.yigit@intel.com>
>> Sent: Thursday, June 14, 2018 9:09 PM
>> To: Ido Goshen <Ido@cgstowernetworks.com>
>> Cc: dev@dpdk.org
>> Subject: Re: [PATCH v2] net/pcap: rx_iface_in stream type support
>>
>> On 6/14/2018 6:14 PM, Ido Goshen wrote:
>>> I use "rx_iface","tx_iface" (and not just "iface") in order to have 
>>> multiple TX queues I just gave a simplified setting with 1 queue My 
>>> app  does a full mesh between the ports (not fixed pairs like l2fwd) 
>>> so all the forwarding lcores can tx to the same port simultaneously and as DPDK docs say:
>>> "Multiple logical cores should never share receive or transmit queues for interfaces since this would require global locks and hinder performance."
>>> For example if I have 3 ports handled by 3 cores it'll be 
>>> 	myapp -c 7 -n1 --no-huge \
>>> 	--vdev=eth_pcap0,rx_iface=eth0,tx_iface=eth0,tx_iface=eth0,tx_iface=eth0 \
>>> 	--vdev=eth_pcap0,rx_iface=eth1,tx_iface=eth1,tx_iface=eth1,tx_iface=eth1 \
>>> 	--vdev=eth_pcap0,rx_iface=eth2,tx_iface=eth2,tx_iface=eth2,tx_iface=eth2 \
>>> 	-- -p 7
>>> Is there another way to achieve multiple queues in pcap vdev?
>>
>> If you want to use multiple core you need multiple queues, as you said, and above is the way to create multiple queues for pcap.
>>
>> Currently "iface" argument only supports single interface in a hardcoded way, but technically it should be possible to update it to support multiple queue.
>>
>> So if "iface" arguments works for you, it can be better to add multi queue support to "iface" instead of introducing a new device argument.
>>
>>>
>>> I do see that using "iface" behaves differently - I'll try to 
>>> investigate why
>>
>> pcap_open_live() is called for both arguments, for "rx_iface/tx_iface" pair it has been called twice one for each. Not sure if pcap library returns same handler or two different handlers for this case since iface name is same.
>> For "iface" argument pcap_open_live() called once, so we have single handler for both Rx & Tx. This may be difference.
>>
>>> And still even when using "iface" I also see packets that are 
>>> transmitted out of eth1 (e.g. tcpreplay -i eth1 packets.pcap) and not 
>>> only packets that are received (e.g. ping from far end to eth0 ip)
>>
>> This is interesting, I have tried with external packet generator, "iface" was working as expected for me.
>>
>>>
>>>
>>> -----Original Message-----
>>> From: Ferruh Yigit <ferruh.yigit@intel.com>
>>> Sent: Wednesday, June 13, 2018 1:57 PM
>>> To: Ido Goshen <Ido@cgstowernetworks.com>
>>> Cc: dev@dpdk.org
>>> Subject: Re: [PATCH v2] net/pcap: rx_iface_in stream type support
>>>
>>> On 6/5/2018 6:10 PM, Ido Goshen wrote:
>>>> The problem is if a dpdk app uses the same iface(s) both as rx_iface and tx_iface then it will receive back the packets it sends.
>>>> If my app sends a packet to portid=X with rte_eth_tx_burst() then I 
>>>> wouldn't expect to receive it back by rte_eth_rx_burst() for that same portid=X  (assuming of course there's no external loopback) This is coming from the default nature of pcap that like a sniffer captures both incoming and outgoing direction.
>>>> The patch provides an option to limit pcap rx_iface to get only incoming traffic which is more like a real (non-pcap) dpdk device.
>>>>
>>>> for example:
>>>> when using existing *rx_iface*
>>>> 	l2fwd -c 3 -n1 --no-huge
>>>> --vdev=eth_pcap0,rx_iface=eth1,tx_iface=eth1
>>>> --vdev=eth_pcap1,rx_iface=dummy0,tx_iface=dummy0  -- -p 3 -T 1 
>>>> sending only 1 single packet into eth1 will end in an infinite loop 
>>>> -
>>>
>>> If you are using same interface for both Rx & Tx, why not using "iface=xxx"
>>> argument, can you please test with following:
>>>
>>> l2fwd -c 3 -n1 --no-huge --vdev=eth_pcap0,iface=eth1
>>> --vdev=eth_pcap1,iface=dummy0 -- -p 3 -T 1
>>>
>>>
>>> I can't reproduce the issue with above command.
>>>
>>> Thanks,
>>> ferruh
>>>
>>
>