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Subject: [RFC] mbuf: performance optimization
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Date: Sun, 21 Jan 2024 06:32:42 +0100
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Thread-Topic: [RFC] mbuf: performance optimization
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From: =?iso-8859-1?Q?Morten_Br=F8rup?= <mb@smartsharesystems.com>
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Cc: <andrew.rybchenko@oktetlabs.ru>
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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 Br=F8rup