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

[Dekel Peled <dekelp@mellanox.com>]

Thanks, PSB.

> -----Original Message-----
> From: Ananyev, Konstantin <konstantin.ananyev@intel.com>
> Sent: Friday, November 8, 2019 3:11 PM
> To: Matan Azrad <matan@mellanox.com>; 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>; 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
> 
> 
> 
> > -----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?
> 

Yes.

> BTW, I think that for ixgbe max lro is RTE_IPV4_MAX_PKT_LEN.

Please see my change in drivers/net/ixgbe/ixgbe_ethdev.c.
Change to RTE_IPV4_MAX_PKT_LEN?

> ixgbe_vf, as I remember, doesn’t support LRO at all.

Please see my change in drivers/net/ixgbe/ixgbe_vf_representor.c
Remove it?

> 
> >
> > > 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?

PMD should use this value and not ignore it.

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