Messages in this thread | | | From | Vivien Didelot <> | Subject | Re: [PATCH/RFC net-next] net: fec: allow "mini jumbo" frames | Date | Sat, 10 Dec 2016 11:55:11 -0500 |
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Hi Nikita,
Nikita Yushchenko <nikita.yoush@cogentembedded.com> writes:
> This adds support for MTU slightly larger than default, on modern > FEC flavours. > > Currently FEC driver uses single hardware Rx buffer per frame. On most > FEC flavours, size of single buffer is limited by 11-bit field, and > has to be multiple of 64 (in the worst case). Thus maximum usable Rx > buffer size is 1984 bytes. > > Of those: > - 2 bytes are used for IP header alignment, > - 14 bytes are used by ethhdr, > - up to 8 bytes are needed for VLAN and/or DSA tags, > - 4 bytes are needed for CRC. > > Thus maximum MTU possible within current RX architecture is 1956. > > This patch allows exactly that. For further increase, Rx architecture > change is needed. > > Use of MTU=1956 gives about 1.5% throughput improvement between two Vybrid > boards, compared to default MTU=1500. > > Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
For what it's worth, I have tested your patch on my ZII Rev B boards (see vf610-zii-dev-rev-b.dts) which have a FEC as the master net device of their DSA trees. They still work as expected.
Tested-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Thanks,
Vivien
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