[dpdk-dev] [patch v3] doc: announce API change in ethdev offload flags

Ananyev, Konstantin konstantin.ananyev at intel.com
Fri Aug 9 10:24:42 CEST 2019


Hi Jerin,

> > > > > Since application has two knobs rte_eth_dev_get_supported_ptypes()
> > > > > and DEV_RX_OFFLOAD_PTYPE. We may not need to new ol_flags for
> > this
> > > > change. Right?
> > > > > i.e if application sets the DEV_RX_OFFLOAD_PTYPE, The application
> > > > > will get the parsed ptypes by the driver(=
> > > > rte_eth_dev_get_supported_ptypes()).
> > > > > So there is no scope ambiguity. Right?
> > > >
> > > > I still think there is:
> > > > Imagine user has 2 eth devices, one does support
> > > > DEV_RX_OFFLOAD_PTYPE, second doesn't.  Now he has a mix of packets
> > > > from both devices, that you want t process.
> > > > How would he figure out for which of them ptype values are valid,
> > > > and for each are not?
> > > > Trace back from what port he has received them?
> > > > Not very convenient, and not always possible.
> > >
> > > I thought so. But in that case, application can always set
> > > DEV_RX_OFFLOAD_PTYPE Flags for all the ethdev ports. Right? Rather
> > > having any complicated ol_flags or port based parsing. If limit the
> > _contract_ to following, we are good. Right?
> > > # when DEV_RX_OFFLOAD_PTYPE is set, mbuf.packet_type will be valid
> > and
> > > mbuf.packet_type will have parsed packet type
> >
> > Yes sure in principle user can calculate smallest common subset of RX
> > offloads supported by all devs in the system and use only  them.
> > Then he can use some global value for ol_flags that will be setup at
> > initialization time, instead of checking ol_flags for every mbuf.
> > Though inside DPDK we don't use that method for other offloads (cksum,
> > vlan, rss).
> > Why we should do different here?
> 
> I agree. We don't need to.
> 
> > Again how to deal with hot-plugged devices with such approach?
> >
> > >
> > > or the negative offload(This contract is pretty clear, I don't think
> > > any ambiguity at all) # when DEV_RX_OFFLOAD_NO_PTYPE(something
> > > similar) is set, mbuf.packet_type will be invalid.
> > >
> > > > I think we need either to introduce new ol_flag value (as we usually
> > > > do for other RX offloads), or force PMD to always set ptype value.
> > >
> > > Setting new  ol_flag value may effect performance for existing drivers
> > > which don't planning to use this offload
> >
> > If the driver doesn't support DEV_RX_OFFLOAD_PTYPE, it wouldn't need to
> > set anything (neither ol_flags, neither packet_type).
> 
> Yes
> 
> >
> > > and it complicates the
> > > application to have additional check based on ol_flag. If you see any
> > > corner case with above section,
> > >
> > > How about just setting as ptype as 0 incase it is not parsed by driver.
> >
> > As I said above - ok by me.
> > AFAIK, this is current behavior, so no changes in PMD will be required.
> >
> > > Actual lookup is the costly one, writing 0 to pytpe is not costly as
> > > there are plenty of writes in Rx and it will be write merged(No CPU
> > > stall)
> >
> > Yes packet_type is at first 64B, so shouldn't cause any extra overhead.
> >
> > >
> > > I did not get the complete picture of
> > > "rte_eth_dev_set_supported_ptypes(uint16_t port_id, uint32_t
> > ptype_mask); instead of DEV_RX_OFFLOAD_PTYPE? scheme", Does it help?
> >
> > I thought about it as just a different way to disable(/limit) requested by user
> > PTYPE support.
> > If let say user is not interested in ptype information at all, he can ask PMD to
> > just always set ptype value to 0:
> > rte_eth_dev_set_supported_ptypes(port, RTE_PTYPE_UNKNOWN);
> >
> > if he is interested just in L2/L3 layer info, he can ask PMD to provide ptype
> > information only for L2/L3:
> > rte_eth_dev_set_supported_ptypes(port, RTE_PTYPE_L2_MASK |
> > RTE_PTYPE_L3_MASK);
> >
> > Or to enable all supported by PMD ptypes:
> > rte_eth_dev_set_supported_ptypes(port, UINT32_MAX)
> 
> 
> The API looks good to me. We need to document the  rte_eth_dev_set_supported_ptypes()
> must  be called when device is in stop state to allow PMD do slow path configuration.
> 
> To summarize:
> Two options to control PTYPE lookup:
> Option 1:
> - If DEV_RX_OFFLOAD_PTYPE set, PMD returns mbuf->packet_type with rte_eth_dev_get_supported_ptypes()
> - If DEV_RX_OFFLOAD_PTYPE is not set, PMD still can return  mbuf->packet_type with rte_eth_dev_get_supported_ptypes()
> But if PMD can do some optimization, it can avoid ptype lookup and return mbuf->packet_type as zero.
> 
> Option 2:
> - Introduce rte_eth_dev_set_supported_ptypes(port, needed_ptypes).

Yes.

> 
> I think, rte_eth_dev_set_supported_ptypes() is better option As Konstantain suggested to
> have selective control of ptype parsing by PMD at the cost of adding new API.
> 
> I think, we can avoid breaking exiting application by, If rte_eth_dev_set_supported_ptypes() is not called,
> PMD must return mbuf->packet_type with rte_eth_dev_get_supported_ptypes().
> If rte_eth_dev_set_supported_ptypes() and successful, PMD must return
> mbuf->packet_type with rte_eth_dev_set_supported_ptypes()

+1

> 
> If there no objection to this API, We can send updated deprecation notice.
> 

None from me.
Konstantin



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