Hi Konstantin

From: Ananyev, Konstantin

Sent: Wednesday, August 7, 2019 1:18 PM
To: Matan Azrad <redacted>; dev@dpdk.org
Cc: Thomas Monjalon <redacted>; Yigit, Ferruh
[off-list ref]; Andrew Rybchenko
[off-list ref]; Olivier Matz [off-list ref]
Subject: RE: [PATCH 2/2] doc: announce new mbuf field for LRO

Hi Matan,

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The API breakage is because the ``tso_segsz`` field was documented
for LRO.

The ``tso_segsz`` field in mbuf indicates the size of each segment
in the LRO packet in Rx path and should be provided by the LRO
packet port.

While the generic LRO packet may aggregate different segments
sizes in one packet, it is impossible to expose this information
for each segment by one field and it doesn't make sense to expose
all the segments sizes in the mbuf.

A new field may be added as union with the above field to expose
the number of segments aggregated in the LRO packet.

Signed-off-by: Matan Azrad <redacted>
---
 doc/guides/rel_notes/deprecation.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/doc/guides/rel_notes/deprecation.rst

b/doc/guides/rel_notes/deprecation.rst
index c0cd9bc..e826b69 100644

--- a/doc/guides/rel_notes/deprecation.rst
+++ b/doc/guides/rel_notes/deprecation.rst

@@ -45,6 +45,10 @@ Deprecation Notices
   - ``eal_parse_pci_DomBDF`` replaced by ``rte_pci_addr_parse``
   - ``rte_eal_compare_pci_addr`` replaced by ``rte_pci_addr_cmp``

+* mbuf: Remove ``tso_segsz`` mbuf field providing for LRO support.
+Use union
+  block for the field memory to be shared with a new field
+``lro_segs_n``
+  indicates the number of segments aggregated in the LRO packet.
+

Wonder how the upper layer will use that information (except for stats)?
Could you guys provide any examples?

1. Stats, allow to calc accurate PPS.
2. Supply accurate information unlike the seg size which cannot be

accurate.

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2. Let the user all the information (segs num allow an average seg
size calculation)

So just for stats, right?

Stats it is one option.

The user configured LRO, means he wants X > 1 packets to be aggregated by the port.

Don't you think X is interesting for the user?

For example, maybe there is Y for the next calculation:

If average(X) < Y:
	Stop LRO - not very good for performance to aggregate small number of packets - stop LRO.
 

If so,  wouldn't it be more plausible to extend PMD itself to provide some
extra statistics?
Just a thought.

Yes, may be interesting but it can be redundant work when the user don't need it.

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Also what PMD should do if HW does supports LRO, but doesn't to
information?

If the PMD knows all the segments size he can calculate it, no?
0 means PMD doesn't support it.

I mean HW/PMD might support LRO, but doesn't provide information about
number of coalesced segments.
What PMD should do in that case?

As I said, to set this field with 0 and set the PKT_RX_LRO flag in ol_flags.
0 in this case means support LRO but cannot supply the segments num.

Do you familiar with PMDs that supports LRO but cannot provide the segments num?
If so, what do these PMDs can provide instead?

Still  set DEV_RX_OFFLOAD_TCP_LRO as enabled RX offload, but don't set
PKT_RX_LRO flag in the RX-ed mbuf, even if it does contain coalesced
packets?

No, read above.

As I understand that what happens now.
It is probably ok by me (as means no changes in ixgbe PMD)...
But wouldn't that mean no defined way for the user to determine will
HW/PMD provide that information or not?

Will compare to 0, see above.

Konstantin

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 * dpaa2: removal of ``rte_dpaa2_memsegs`` structure which has
been

replaced

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   by a pa-va search library. This structure was earlier being used for

holding

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   memory segments used by dpaa2 driver for faster pa->va translation.
This
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