On 09/05/14 23:19, Eric Joyner wrote:
There are some concerns if we use this with devices that ixl supports:
- The maximum fragment size is 16KB-1, which isn't a power of 2.
Multiplying by powers of two are more fast, than non-powers of two. So
in this case you would have to use 8KB as a maximum.
- You can't get the maximum TSO size for ixl devices by multiplying the
maximum number of fragments by the maximum size.
Instead the number of fragments is AFAIK unlimited, but a segment can only
span 8 mbufs (including the [up to 3] mbufs containing the header), and the
maximum TSO size is 256KB.
And one question:
- Is hdr_size_log2 supposed to be the length of the L2 header? We can fit
254 L2 bytes in our hardware during a TSO, so if that's the value, I guess
that's fine, barring the it-not-being-a-power-of-2 issue.
This is the ethernet / vlan headers. It is added with the TCP/IP-header
in the end.
With all that said, the 8 mbuf limit per segment issue is a TSO limitation
that we'd like to notify the stack about, so I wonder if that could be
incorporated along with this. Right now, our driver checks to see if a
segment in a TSO spans more than six mbufs and then m_defrag()'s the entire
chain if one exists; it's less than optimal but necessary to prevent errors.
It is not impossible to move from log2 syntax to non-log2 syntax, hence
the logic will be exactly the same, only that the required division and
multiplication will have a bit overhead I guess.
Could you make a patch on top of my patch with the changes you think are
required to fully support the ixl hardware? Or propose a new patch which
also serves the MLX needs?
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