[RFC] mbuf: performance optimization

[Morten Brørup]

What is the largest realistic value of mbuf->priv_size (the size of an mbuf's application private data area) in any use case?

I am wondering if its size could be reduced from 16 to 8 bit. If a max value of 255 isn't enough, then perhaps by knowing that the private data area must be aligned by 8 (RTE_MBUF_PRIV_ALIGN), its value can hold the size divided by 8. That would make the max value nearly 2 KB.

I suppose that reducing mbuf->nb_segs from 16 to 8 bit is realistic, considering that a maximum size IP packet (64 KB) is unlikely to use more than 64 plus some segments. Does anyone know of any use case with more than 255 segments in an mbuf?

These two changes would allow us to move mbuf->priv_size from the second to the first cache line.


Furthermore, mbuf->timesync should be a dynamic field. This, along with the above changes, would give us one more available 32-bit dynamic field.


Med venlig hilsen / Kind regards,
-Morten Brørup