Re: [dpdk-dev] [PATCH v2] net/pcap: enable data path on secondary

["Zhang, Qi Z" <qi.z.zhang@intel.com>]

> -----Original Message-----
> From: Yigit, Ferruh
> Sent: Tuesday, November 13, 2018 10:44 AM
> To: Zhang, Qi Z <qi.z.zhang@intel.com>; Thomas Monjalon
> <thomas@monjalon.net>
> Cc: dev@dpdk.org; Lin, Xueqin <xueqin.lin@intel.com>
> Subject: Re: [PATCH v2] net/pcap: enable data path on secondary
> 
> On 11/13/2018 6:27 PM, Zhang, Qi Z wrote:
> > First, apologies to make this in rush since I was somehow under pressure to
> make pdump works in 18.11.
> > I agree there is lot of things need to improve, but the strategy here
> > is to make it work quietly and not break anything else :) add some
> comments inline.
> >
> >> -----Original Message-----
> >> From: Thomas Monjalon [mailto:thomas@monjalon.net]
> >> Sent: Tuesday, November 13, 2018 9:15 AM
> >> To: Yigit, Ferruh <ferruh.yigit@intel.com>; Zhang, Qi Z
> >> <qi.z.zhang@intel.com>
> >> Cc: dev@dpdk.org; Lin, Xueqin <xueqin.lin@intel.com>
> >> Subject: Re: [PATCH v2] net/pcap: enable data path on secondary
> >>
> >> Just a quick comment:
> >> There are probably some ideas to take from what was done for tap.
> >
> >>
> >>
> >> 13/11/2018 17:56, Ferruh Yigit:
> >>> On 11/12/2018 4:51 PM, Qi Zhang wrote:
> >>>> Private vdev on secondary is never supported by the new shared
> >>>> device mode but pdump still relies on a private pcap PMD on
> secondary.
> >>>> The patch enables pcap PMD's data path on secondary so that pdump
> >>>> can work as usual.
> >>>
> >>> It would be great if you described the problem a little more.
> >>>
> >>> Private vdev was the way previously, when pdump developed, now with
> >>> shared device mode on virtual devices, pcap data path in secondary
> >>> is not
> >> working.
> >>>
> >>> What exactly not working is (please correct me if I am wrong):
> >>> When secondary adds a virtual device, related data transferred to
> >>> primary and primary creates the device and shares device back with
> >> secondary.
> >>> When pcap device created in primary, pcap handlers (pointers) are
> >>> process local and they are not valid for secondary process. This
> >>> breaks
> >> secondary.
> >>>
> >>> So we can't directly share the pcap handlers, but need to create a
> >>> new set of handlers for secondary, that is what you are doing in
> >>> this patch, although I have some comments, please check below.
> >>>
> >>> Since there is single storage for pcap handlers that primary and
> >>> secondary shares and they can't share the handlers, you can't make
> >>> both primary and secondary data path work. Also freeing handlers is
> >>> another concern. What is needed is `rte_eth_dev->process_private`
> >>> which
> >> has been added in this release.
> >
> > You are right, we should prevent handler be opened in primary be
> corrupted during probe at secondary.
> > Now, I see this problem in pcap , as an example:
> > internals->tx_queue[i].dumper/pcap is shared but will be overwritten
> > at secondary, we should fix them by use process_private,
> >
> >>>
> >>>>
> >>>> Signed-off-by: Qi Zhang <qi.z.zhang@intel.com>
> >>>> Tested-by: Yufeng Mo <yufengx.mo@intel.com>
> >>>
> >>> <...>
> >>>
> >>>> @@ -934,6 +935,10 @@ pmd_init_internals(struct rte_vdev_device
> >> *vdev,
> >>>>  	 */
> >>>>  	(*eth_dev)->dev_ops = &ops;
> >>>>
> >>>> +	/* store a copy of devargs for secondary process */
> >>>> +	strlcpy(internals->devargs, rte_vdev_device_args(vdev),
> >>>> +			ETH_PCAP_ARG_MAXLEN);
> >>>
> >>> Why we need to cover this in PMD level?
> >>>
> >>> Why secondary probe isn't getting devargs? Can't we fix this in eal level?
> >>> It can be OK to workaround in the PMD taking account of the time of
> >>> the release, but for long term I think this should be fixed in eal.
> >
> > Yes this is the workaround for quick fix.
> > Ideally secondary process should not take care of devargs, it just attach.
> > And it's better to only parse devargs on one process ( primary process), the
> parsed result could be stored to intermediate result in shared
> memory,(examples, internal->nb_rx_queue_required) so secondary process
> don't need to parse it again.
> >>>
> >>> <...>
> >>>
> >>>> @@ -1122,23 +1126,37 @@ pmd_pcap_probe(struct rte_vdev_device
> >> *dev)
> >>>>  	start_cycles = rte_get_timer_cycles();
> >>>>  	hz = rte_get_timer_hz();
> >>>>
> >>>> -	if (rte_eal_process_type() == RTE_PROC_SECONDARY) {
> >>>> +	if (rte_eal_process_type() == RTE_PROC_PRIMARY) {
> >>>> +		kvlist = rte_kvargs_parse(rte_vdev_device_args(dev),
> >>>> +				valid_arguments);
> >>>> +		if (kvlist == NULL)
> >>>> +			return -EINVAL;
> >>>> +		if (rte_kvargs_count(kvlist, ETH_PCAP_IFACE_ARG) == 1)
> >>>> +			nb_rx_queue = 1;
> >>>> +		else
> >>>> +			nb_rx_queue =
> >>>> +				rte_kvargs_count(kvlist,
> >>>> +					ETH_PCAP_RX_PCAP_ARG) ? 1 : 0;
> >>>> +		nb_tx_queue = 1;
> >>>
> >>> This part is wrong. pcap pmd supports multi queue, you can't
> >>> hardcode the number of queues. Also for Tx why it ignores `rx_iface`
> argument?
> >>> This is just hacking the driver for a specific use case breaking others.
> >
> > Previously the nb_tx_queue and nb_rx_queue is decided by
> pcaps.num_of_queue and dumpers.num_of_queues.
> > I just can't figure out a way that we can have more than 1 queue during
> probe, look at below code.
> >
> > If ETH_PCAP_IFACE_ARG
> >
> > 	pcaps.num_of_queue = 1;
> > 	dumpers.num_of_queue = 1;
> >
> > else
> > 	is_rx_pcap = rte_kvargs_count(kvlist, ETH_PCAP_RX_PCAP_ARG) ? 1 : 0;
> >         pcaps.num_of_queue = 0;
> > 	if (is_rx_pcap) {
> >                 ret = rte_kvargs_process(kvlist,
> ETH_PCAP_RX_PCAP_ARG,
> >                                 &open_rx_pcap, &pcaps);
> >
> > 				// pcaps.num_of_queue = 1;
> >         } else {
> >                 ret = rte_kvargs_process(kvlist, NULL,
> >                                 &rx_iface_args_process, &pcaps);
> > 				// pcaps.num_of_queue = 0;
> >         }
> >
> > 		is_tx_pcap = rte_kvargs_count(kvlist, ETH_PCAP_TX_PCAP_ARG) ?
> 1 : 0;
> >         dumpers.num_of_queue = 0;
> >
> >         if (is_tx_pcap)
> >                 ret = rte_kvargs_process(kvlist,
> ETH_PCAP_TX_PCAP_ARG,
> >                                 &open_tx_pcap, &dumpers);
> > 				// dumpers.num_of_queue = 1
> >         else
> >                 ret = rte_kvargs_process(kvlist,
> ETH_PCAP_TX_IFACE_ARG,
> >                                 &open_tx_iface, &dumpers);
> > 				// dumpers.num_of_queue = 1
> >
> > That's the same logic I applied, did I missed something, would you explain
> more for this?
> 
> ETH_PCAP_IFACE_ARG is "iface=xxx" usage, both Rx and Tx use the same
> interface, because of implementation limitation it only supports 1 queue.
> 
> rx_pcap, rx_iface, rx_iface_in supports multiple queues, by providing them
> multiple time. Like "rx_pcap=q1.pcap,rx_pcap=q2.pcap,rx_pcap=q3.pcap"
> will create 3 Rx queues each having their own .pcap file. Same is valid for Tx.
> 
> rte_kvargs_process() calls callback function per argument provided, so if an
> argument provided multiple times, it will call same callback multiple times,
> that is why 'num_of_queue' increased in callback functions.

Ok, this is what I missed, I didn't notice pcap devargs will take advantage by using the same key for multiple times.

BTW, I also noticed it may not necessary to estimate the queue number and call pmd_init_internals before open any pcap file or iface as you mentioned.
The reason I have this is, previously I worried about if a pcap file can be locked by one process and prevent another process to access it, so I think about to add "owner" to in devargs to make sure only one process will access the files, but after I figure out this is not necessary, the queue estimation part should be removed and rollback to a simple solution as you suggested. 

Thanks for the help!
Qi

> 
> In high-level, pmd_pcap_probe() first parses the arguments and creates pcap
> handlers based on arguments, later as a last thing creates ethdev using these
> information. I am for keeping this logic, doing something different for
> secondary can cause issues in edge cases not obvious at first look.
> 
> >
> > Thanks
> > Qi
> >
> >>>
> >>>> +		ret = pmd_init_internals(dev, nb_rx_queue,
> >>>> +				nb_tx_queue, &eth_dev);
> >>>
> >>> I think it is not required to move pmd_init_internals() here.
> >>> This can be done simpler, I will send a draft patch as a reply to
> >>> this mail for possible solution.
> >>> But again that can't be final solution, we need to use
> >>> `process_private`
> >>>
> >>> <...>
> >>>
> >>
> >>
> >>
> >>
> >