[dpdk-dev] [PATCH v4 3/5] net/ice: fix max mtu size packets with vlan tag cannot be received by default

[Ananyev, Konstantin]

> >>>>>>>>>
> >>>>>>>>> testpmd will initialize default max packet length to 1518 which
> >>>>>>>>> doesn't include vlan tag size in ether overheader. Once, send the
> >>>>>>>>> max mtu length packet with vlan tag, the max packet length will
> >>>>>>>>> exceed 1518 that will cause packets dropped directly from NIC hw
> >>>>> side.
> >>>>>>>>>
> >>>>>>>>> ice can support dual vlan tags that need more 8 bytes for max
> >>>>>>>>> packet size, so, configures the correct max packet size in
> >>>>>>>>> dev_config
> >>>>>> ops.
> >>>>>>>>>
> >>>>>>>>> Fixes: 50cc9d2a6e9d ("net/ice: fix max frame size")
> >>>>>>>>>
> >>>>>>>>> Signed-off-by: SteveX Yang <stevex.yang at intel.com>
> >>>>>>>>> ---
> >>>>>>>>>    drivers/net/ice/ice_ethdev.c | 11 +++++++++++
> >>>>>>>>>    1 file changed, 11 insertions(+)
> >>>>>>>>>
> >>>>>>>>> diff --git a/drivers/net/ice/ice_ethdev.c
> >>>>>>>>> b/drivers/net/ice/ice_ethdev.c index
> >>>>>>>>> cfd357b05..6b7098444 100644
> >>>>>>>>> --- a/drivers/net/ice/ice_ethdev.c
> >>>>>>>>> +++ b/drivers/net/ice/ice_ethdev.c
> >>>>>>>>> @@ -3146,6 +3146,7 @@ ice_dev_configure(struct rte_eth_dev
> >>> *dev)
> >>>>>>>>> struct ice_adapter *ad =
> >>>>>>>>> ICE_DEV_PRIVATE_TO_ADAPTER(dev->data->dev_private);
> >>>>>>>>>    struct ice_pf *pf =
> >>>>>>>>> ICE_DEV_PRIVATE_TO_PF(dev->data->dev_private);
> >>>>>>>>> +uint32_t frame_size = dev->data->mtu + ICE_ETH_OVERHEAD;
> >>>>>>>>>    int ret;
> >>>>>>>>>
> >>>>>>>>>    /* Initialize to TRUE. If any of Rx queues doesn't meet the @@
> >>>>>>>>> -3157,6
> >>>>>>>>> +3158,16 @@ ice_dev_configure(struct rte_eth_dev *dev)
> >>>>>>>>>    if (dev->data->dev_conf.rxmode.mq_mode &
> >>> ETH_MQ_RX_RSS_FLAG)
> >>>>>>>>> dev->data->dev_conf.rxmode.offloads |=
> >>>>>> DEV_RX_OFFLOAD_RSS_HASH;
> >>>>>>>>>
> >>>>>>>>> +/**
> >>>>>>>>> + * Considering QinQ packet, max frame size should be equal or
> >>>>>>>>> + * larger than total size of MTU and Ether overhead.
> >>>>>>>>> + */
> >>>>>>>>
> >>>>>>>>> +if (frame_size > dev->data->dev_conf.rxmode.max_rx_pkt_len) {
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Why we need this check?
> >>>>>>>> Can we just call ice_mtu_set directly
> >>>>>>>
> >>>>>>> I think that without that check we can silently overwrite provided
> >>>>>>> by user dev_conf.rxmode.max_rx_pkt_len value.
> >>>>>>
> >>>>>> OK, I see
> >>>>>>
> >>>>>> But still have one question
> >>>>>> dev->data->mtu is initialized to 1518 as default , but if
> >>>>>> dev->data->application set
> >>>>>> dev_conf.rxmode.max_rx_pkt_len = 1000 in dev_configure.
> >>>>>> does that mean we will still will set mtu to 1518, is this expected?
> >>>>>>
> >>>>>
> >>>>> max_rx_pkt_len should be larger than mtu at least, so we should raise
> >>>>> the max_rx_pkt_len (e.g.:1518) to hold expected mtu value (e.g.: 1500).
> >>>>
> >>>> Ok, this describe the problem more general and better to replace exist
> >>> code comment and commit log for easy understanding.
> >>>> Please send a new version for reword
> >>>>
> >>>
> >>> I didn't really get this set.
> >>>
> >>> Application explicitly sets 'max_rx_pkt_len' to '1518', and a frame bigger than
> >>> this size is dropped.
> >>
> >> Sure, it is normal case for dropping oversize data.
> >>
> >>> Isn't this what should be, why we are trying to overwrite user configuration
> >>> in PMD to prevent this?
> >>>
> >>
> >> But it is a confliction that application/user sets mtu & max_rx_pkt_len at the same time.
> >> This fix will make a decision when confliction occurred.
> >> MTU value will come from user operation (e.g.: port config mtu 0 1500) directly,
> >> so, the max_rx_pkt_len will resize itself to adapt expected MTU value if its size is smaller than MTU + Ether overhead.
> >>
> >>> During eth_dev allocation, mtu set to default '1500', by ethdev layer.
> >>> And testpmd sets 'max_rx_pkt_len' by default to '1518'.
> >>> I think Qi's concern above is valid, what is user set 'max_rx_pkt_len' to '1000'
> >>> and mean it? PMD will not honor the user config.
> >>
> >> I'm not sure when set 'mtu' to '1500' and 'max_rx_pkt_len' to '1000', what's the behavior expected?
> >> If still keep the 'max_rx_pkt_len' value, that means the larger 'mtu' will be invalid.
> >>
> >>>
> >>> Why not simply increase the default 'max_rx_pkt_len' in testpmd?
> >>>
> >> The default 'max_rx_pkt_len' has been initialized to generical value (1518) and default 'mtu' is '1500' in testpmd,
> >> But it isn't suitable to those NIC drivers which Ether overhead is larger than 18. (e.g.: ice, i40e) if 'mtu' value is preferable.
> >>
> >>> And I guess even better what we need is to tell to the application what the
> >>> frame overhead PMD accepts.
> >>> So the application can set proper 'max_rx_pkt_len' value per port for a
> >>> given/requested MTU value.
> >>> @Ian, cc'ed, was complaining almost same thing years ago, these PMD
> >>> overhead macros and 'max_mtu'/'min_mtu' added because of that, perhaps
> >>> he has a solution now?
> >
> >  From my perspective the main problem here:
> > We have 2 different variables for nearly the same thing:
> > rte_eth_dev_data.mtu and rte_eth_dev_data.dev_conf.max_rx_pkt_len.
> > and 2 different API to update them: dev_mtu_set() and dev_configure().
> 
> According API 'max_rx_pkt_len' is 'Only used if JUMBO_FRAME enabled'
> Although not sure that is practically what is done for all drivers.

I think most of Intel PMDs use it unconditionally.

> 
> > And inside majority of Intel PMDs we don't keep these 2 variables in sync:
> > - mtu_set() will update both variables.
> > - dev_configure() will update only max_rx_pkt_len, but will keep mtu intact.
> >
> > This patch fixes this inconsistency, which I think is a good thing.
> > Though yes, it introduces change in behaviour.
> >
> > Let say the code:
> > rte_eth_dev_set_mtu(port, 1500);
> > dev_conf.max_rx_pkt_len = 1000;
> > rte_eth_dev_configure(port, 1, 1, &dev_conf);
> >
> 
> 'rte_eth_dev_configure()' is one of the first APIs called, it is called before
> 'rte_eth_dev_set_mtu().

Usually yes. 
But you can still do sometimes later: dev_mtu_set(); ...; dev_stop(); dev_configure(); dev_start();

> 
> When 'rte_eth_dev_configure()' is called, MTU is set to '1500' by default by
> ethdev layer, so it is not user configuration, but 'max_rx_pkt_len' is.

See above.
PMD doesn't know where this MTU value came from (default ethdev value or user specified value)
and probably it shouldn't care.

>
> And later, when 'rte_eth_dev_set_mtu()' is called, but MTU and 'max_rx_pkt_len'
> are updated (mostly).

Yes, in mtu_set() we update both.
But we don't update MTU in dev_configure(), only max_rx_pkt_len.
That what this patch tries to fix (as I understand it).

> 
> 
> > Before the patch will result:
> > mtu==1500, max_rx_pkt_len=1000;  //out of sync looks wrong to me
> >
> > After the patch:
> > mtu=1500, max_rx_ptk_len=1518; // in sync, change in behaviour.
> >
> > If you think we need to preserve current behaviour,
> > then I suppose the easiest thing would be to change dev_config() code
> > to update mtu value based on max_rx_pkt_len.
> > I.E: dev_configure {...; mtu_set(max_rx_pkt_len - OVERHEAD); ...}
> > So the code snippet above will result:
> > mtu=982,max_rx_pkt_len=1000;
> >
> 
> The 'max_rx_ptk_len' is annoyance for a long time, what do you think to just
> drop it?
>
> By default device will be up with default MTU (1500), later
> 'rte_eth_dev_set_mtu' can be used to set the MTU, no frame size setting at all.
> 
> Will this work?

I think it might, but that's a big change, probably too risky at that stage...
 

> 
> 
> And for short term, for above Intel PMDs, there must be a place this
> 'max_rx_pkt_len' value taken into account (mostly 'start()' dev_ops), that
> function can be updated to take 'max_rx_pkt_len' only if JUMBO_FRAME set,
> otherwise use the 'MTU' value.

Even if we'll use max_rx_pkt_len only when if JUMBO_FRAME is set,
I think we still need to keep max_rx_pkt_len and MTU values in sync. 

> 
> Without 'start()' updated the current logic won't work after stop & start anyway.
> 
> 
> >
> >
> >
> >>
> >>>
> >>> And why this same thing can't happen to other PMDs? If this is a problem for
> >>> all PMDs, we should solve in other level, not for only some PMDs.
> >>>
> >> No, all PMDs exist the same issue, another proposal:
> >>   -  rte_ethdev provides the unique resize 'max_rx_pkt_len' in rte_eth_dev_configure();
> >>   - provide the uniform API for fetching the NIC's supported Ether Overhead size;
> >> Is it feasible?
> >>
> >>>>
> >>>>> Generally, the mtu value can be adjustable from user (e.g.: ip link
> >>>>> set ens801f0 mtu 1400), hence, we just adjust the max_rx_pkt_len to
> >>>>> satisfy mtu requirement.
> >>>>>
> >>>>>> Should we just call ice_mtu_set(dev, dev_conf.rxmode.max_rx_pkt_len)
> >>>>>> here?
> >>>>> ice_mtu_set(dev, mtu) will append ether overhead to
> >>>>> frame_size/max_rx_pkt_len, so we need pass the mtu value as the 2nd
> >>>>> parameter, or not the max_rx_pkt_len.
> >>>>>
> >>>>>>
> >>>>>>
> >>>>>>>
> >>>>>>>> And please remove above comment, since ether overhead is already
> >>>>>>> considered in ice_mtu_set.
> >>>>> Ether overhead is already considered in ice_mtu_set, but it also
> >>>>> should be considered as the adjustment condition that if ice_mtu_set
> >>> need be invoked.
> >>>>> So, it perhaps should remain this comment before this if() condition.
> >>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>>> +ret = ice_mtu_set(dev, dev->data->mtu); if (ret != 0) return
> >>>>>>>>> +ret; }
> >>>>>>>>> +
> >>>>>>>>>    ret = ice_init_rss(pf);
> >>>>>>>>>    if (ret) {
> >>>>>>>>>    PMD_DRV_LOG(ERR, "Failed to enable rss for PF");
> >>>>>>>>> --
> >>>>>>>>> 2.17.1
> >>>>>>>>
> >>>>>>>
> >>>>>>
> >>>>>
> >>>>
> >