[dpdk-dev] [PATCH v4 1/3] ethdev: support API to set max LRO packet size

[Dekel Peled]

Thanks, PSB.

> -----Original Message-----
> From: Ferruh Yigit <ferruh.yigit at intel.com>
> Sent: Friday, November 8, 2019 2:52 PM
> To: Matan Azrad <matan at mellanox.com>; Dekel Peled
> <dekelp at mellanox.com>; john.mcnamara at intel.com;
> marko.kovacevic at intel.com; nhorman at tuxdriver.com;
> ajit.khaparde at broadcom.com; somnath.kotur at broadcom.com;
> anatoly.burakov at intel.com; xuanziyang2 at huawei.com;
> cloud.wangxiaoyun at huawei.com; zhouguoyang at huawei.com;
> wenzhuo.lu at intel.com; konstantin.ananyev at intel.com; Shahaf Shuler
> <shahafs at mellanox.com>; Slava Ovsiienko <viacheslavo at mellanox.com>;
> rmody at marvell.com; shshaikh at marvell.com;
> maxime.coquelin at redhat.com; tiwei.bie at intel.com;
> zhihong.wang at intel.com; yongwang at vmware.com; Thomas Monjalon
> <thomas at monjalon.net>; arybchenko at solarflare.com;
> jingjing.wu at intel.com; bernard.iremonger at intel.com
> Cc: dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v4 1/3] ethdev: support API to set max LRO
> packet size
> 
> On 11/8/2019 11:56 AM, Matan Azrad wrote:
> >
> >
> > From: Ferruh Yigit
> >> On 11/8/2019 10:10 AM, Matan Azrad wrote:
> >>>
> >>>
> >>> From: Ferruh Yigit
> >>>> On 11/8/2019 6:54 AM, Matan Azrad wrote:
> >>>>> Hi
> >>>>>
> >>>>> From: Ferruh Yigit
> >>>>>> On 11/7/2019 12:35 PM, Dekel Peled wrote:
> >>>>>>> @@ -1266,6 +1286,18 @@ struct rte_eth_dev *
> >>>>>>>
> >>>>>> 	RTE_ETHER_MAX_LEN;
> >>>>>>>  	}
> >>>>>>>
> >>>>>>> +	/*
> >>>>>>> +	 * If LRO is enabled, check that the maximum aggregated
> >> packet
> >>>>>>> +	 * size is supported by the configured device.
> >>>>>>> +	 */
> >>>>>>> +	if (dev_conf->rxmode.offloads &
> >> DEV_RX_OFFLOAD_TCP_LRO) {
> >>>>>>> +		ret = check_lro_pkt_size(
> >>>>>>> +				port_id, dev_conf-
> >>>>>>> rxmode.max_lro_pkt_size,
> >>>>>>> +				dev_info.max_lro_pkt_size);
> >>>>>>> +		if (ret != 0)
> >>>>>>> +			goto rollback;
> >>>>>>> +	}
> >>>>>>> +
> >>>>>>
> >>>>>> This check forces applications that enable LRO to provide
> >>>> 'max_lro_pkt_size'
> >>>>>> config value.
> >>>>>
> >>>>> Yes.(we can break an API, we noticed it)
> >>>>
> >>>> I am not talking about API/ABI breakage, that part is OK.
> >>>> With this check, if the application requested LRO offload but not
> >>>> provided 'max_lro_pkt_size' value, device configuration will fail.
> >>>>
> >>> Yes
> >>>> Can there be a case application is good with whatever the PMD can
> >>>> support as max?
> >>> Yes can be - you know, we can do everything we want but it is better
> >>> to be
> >> consistent:
> >>> Due to the fact of Max rx pkt len field is mandatory for JUMBO
> >>> offload, max
> >> lro pkt len should be mandatory for LRO offload.
> >>>
> >>> So your question is actually why both, non-lro packets and LRO
> >>> packets max
> >> size are mandatory...
> >>>
> >>>
> >>> I think it should be important values for net applications management.
> >>> Also good for mbuf size managements.
> >>>
> >>>>>
> >>>>>> - Why it is mandatory now, how it was working before if it is
> >>>>>> mandatory value?
> >>>>>
> >>>>> It is the same as max_rx_pkt_len which is mandatory for jumbo
> >>>>> frame
> >>>> offload.
> >>>>> So now, when the user configures a LRO offload he must to set max
> >>>>> lro pkt
> >>>> len.
> >>>>> We don't want to confuse the user here with the max rx pkt len
> >>>> configurations and behaviors, they should be with same logic.
> >>>>>
> >>>>> This parameter defines well the LRO behavior.
> >>>>> Before this, each PMD took its own interpretation to what should
> >>>>> be the
> >>>> maximum size for LRO aggregated packets.
> >>>>> Now, the user must say what is his intension, and the ethdev can
> >>>>> limit it
> >>>> according to the device capability.
> >>>>> By this way, also, the PMD can organize\optimize its data-path more.
> >>>>> Also, the application can create different mempools for LRO queues
> >>>>> to
> >>>> allow bigger packet receiving for LRO traffic.
> >>>>>
> >>>>>> - What happens if PMD doesn't provide 'max_lro_pkt_size', so it is
> '0'?
> >>>>> Yes, you can see the feature description Dekel added.
> >>>>> This patch also updates all the PMDs support an LRO for non-0 value.
> >>>>
> >>>> Of course I can see the updates Matan, my point is "What happens if
> >>>> PMD doesn't provide 'max_lro_pkt_size'",
> >>>> 1) There is no check for it right, so it is acceptable?
> >>>
> >>> There is check.
> >>> If the capability is 0, any non-zero configuration will fail.
> >>>
> >>>> 2) Are we making this filed mandatory to provide for PMDs, it is
> >>>> easy to make new fields mandatory for PMDs but is this really
> necessary?
> >>>
> >>> Yes, for consistence.
> >>>
> >>>>>
> >>>>> as same as max rx pkt len, no?
> >>>>>
> >>>>>> - What do you think setting 'max_lro_pkt_size' config value to
> >>>>>> what PMD provided if application doesn't provide it?
> >>>>> Same answers as above.
> >>>>>
> >>>>
> >>>> If application doesn't care the value, as it has been till now, and
> >>>> not provided explicit 'max_lro_pkt_size', why not ethdev level use
> >>>> the value provided by PMD instead of failing?
> >>>
> >>> Again, same question we can ask on max rx pkt len.
> >>>
> >>> Looks like the packet size is very important value which should be
> >>> set by
> >> the application.
> >>>
> >>> Previous applications have no option to configure it, so they
> >>> haven't
> >> configure it, (probably cover it somehow) I think it is our miss to
> >> supply this info.
> >>>
> >>> Let's do it in same way as we do max rx pkt len (as this patch main idea).
> >>> Later, we can change both to other meaning.
> >>>
> >>
> >> I think it is not a good reason to introduce a new mandatory config
> >> option for application because of 'max_rx_pkt_len' does it.
> >
> > It is mandatory only if LRO offload is configured.
> >
> >> Will it work, if:
> >> - If application doesn't provide this value, use the PMD max
> >
> > May cause a problem if the mbuf size is not enough for the PMD maximum.
> 
> OK, this is what I was missing, for this case I was thinking max_rx_pkt_len will
> be used but you already explained that application may want to use different
> mempools for LRO queues.
> 
> For this case shouldn't PMDs take the 'rxmode.max_lro_pkt_size' into
> account and program the device accordingly (of course in LRO enabled case)
> ?
> This part seems missing and should be highlighted to other PMD maintainers.
> 

All relevant PMDs were modified and maintainers are copied on this patch series.

> >
> >> - If both application and PMD doesn't provide this value, fail on
> configure()?
> >
> > It will work.
> > In my opinion - not ideal.
> >
> > Matan
> >
> >