[dpdk-dev] [PATCH 01/12] ethdev: add API to query what/if packet type is set

[Adrien Mazarguil]

On Tue, Jan 05, 2016 at 04:50:31PM +0000, Ananyev, Konstantin wrote:
[...]
> > -----Original Message-----
> > From: Nélio Laranjeiro [mailto:nelio.laranjeiro at 6wind.com]
[...]
> > I think we miss a comment here in how those 2/6/4 values are chosen
> > because, according to the mask, I expect 16 possibilities but I get
> > less.  It will help a lot anyone who needs to add a new type.
> > 
> > Extending the snprintf behavior above, it is best to remove the mask
> > argument altogether and have rte_eth_dev_get_ptype_info() return the
> > entire list every time.  Applications need to iterate on the result in
> > any case.
> 
> I think we'd better keep mask argument.
> In many cases upper layer only interested in some particular  subset of
> all packet types that HW can recognise.
> Let say l3fwd only cares about  RTE_PTYPE_L3_MASK, it is not interested in L4,
> tunnelling packet types, etc.
> If caller needs to know all recognised ptypes, he can set mask==-1,
> In that case all supported packet types will be returned.

There are other drawbacks to the mask argument in my opinion. The API will
have to be updated again as soon as 32 bits aren't enough to represent all
possible masks. We can't predict it will be large enough forever but on the
other hand, using uint64_t seems overkill at this point.

I think this use for masks should be avoided when performance does not
matter much, as in this case, user application cannot know the number of
entries in advance and must rely on the returned value to iterate.

A helper function can be added to convert a RTE_PTYPE_* value to the layer
it belongs to (using enum to define possible values).

If we absolutely want a mean to filter returned values, I suggest we use
this enum instead of the mask argument. Since it won't be a mask, it won't
have to be updated every time a new protocol requires extending one.

> >   rte_eth_dev_get_ptype_info(uint8_t port_id, uint32_t ptypes[],
> >                              size_t max_entries)
> > 
> > 
> > 
> > Another point, I have read the example patch (l3fwd) but I don't
> > understand why the PMD is not responsible for filling the packet type in
> > the MBUF (packet parsing is done by parse_packet_type()).  Why the extra
> > computation?
> 
> As I understand there are 3 possibilities now:
> 1. HW supports ptype recognition and SW ptype parsing is never done
> (--parse-ptype is not specified).
> 2. HW supports ptype recognition, but and SW ptype parsing is done anyway
> (--parse-ptype is specified).
> 3. HW doesn't support and ptype recognition, and and SW ptype parsing is done
> (--parse-ptype is specified).
> 
> I suppose the question is what for introduce '--parse-ptype' at all?
> My thought because of #2, so people can easily check what will be the performance impact of SW parsing. 
> 
> Konstantin
> 
> > 
> > I see it more like an offload request (as checksum, etc...) and if the
> > NIC does not support it then the application does the necessary overload.
> > 
> > Best regards,
> > 
> > --
> > Nélio Laranjeiro
> > 6WIND

-- 
Adrien Mazarguil
6WIND