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

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> -----Original Message-----
> From: Matan Azrad <matan@mellanox.com>
> Sent: Friday, November 8, 2019 11:56 AM
> To: Yigit, Ferruh <ferruh.yigit@intel.com>; Dekel Peled <dekelp@mellanox.com>; Mcnamara, John <john.mcnamara@intel.com>;
> Kovacevic, Marko <marko.kovacevic@intel.com>; nhorman@tuxdriver.com; ajit.khaparde@broadcom.com;
> somnath.kotur@broadcom.com; Burakov, Anatoly <anatoly.burakov@intel.com>; xuanziyang2@huawei.com;
> cloud.wangxiaoyun@huawei.com; zhouguoyang@huawei.com; Lu, Wenzhuo <wenzhuo.lu@intel.com>; Ananyev, Konstantin
> <konstantin.ananyev@intel.com>; Shahaf Shuler <shahafs@mellanox.com>; Slava Ovsiienko <viacheslavo@mellanox.com>;
> rmody@marvell.com; shshaikh@marvell.com; maxime.coquelin@redhat.com; Bie, Tiwei <tiwei.bie@intel.com>; Wang, Zhihong
> <zhihong.wang@intel.com>; yongwang@vmware.com; Thomas Monjalon <thomas@monjalon.net>; arybchenko@solarflare.com; Wu,
> Jingjing <jingjing.wu@intel.com>; Iremonger, Bernard <bernard.iremonger@intel.com>
> Cc: dev@dpdk.org
> Subject: RE: [dpdk-dev] [PATCH v4 1/3] ethdev: support API to set max LRO packet size
> 
> 
> 
> 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.

So max_rx_pkt_len will remain max size of one packet,
while max_lro_len will be max accumulate size for each LRO session?

BTW, I think that for ixgbe max lro is RTE_IPV4_MAX_PKT_LEN.
ixgbe_vf, as I remember, doesn’t support LRO at all.

> 
> > 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.

Another question, what will happen if PMD will ignore that value and will
generate packets bigger then requested?

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