64K NFS I/O generates a 34mbuf list for TCP which breaks TSO

[Rick Macklem]

Adrian Chadd wrote:
> On 30 January 2014 07:06, Rick Macklem <rmacklem at uoguelph.ca> wrote:
> > Hi, just adding one more idea on what to do about this
> > to the list:
> > - Add a if_hw_tsomaxseg and modify the loop in tcp_output()
> >   so that it uses both if_hw_tsomax and if_hw_tsomaxseg to
> >   decide how much to hand to the device driver in each mbuf list.
> >   (I haven't looked to see how easy it would be to change this
> >   loop.)
> 
> I don't think that's a hack. I think adding that and setting
> tsomaxseg
> to say 30 for now would be a good comprimise.
> 
Well, my TCP is very rusty and I have no way to test it (I don't
have anything that does TSO), but I've attached a stab at a patch
to do this.

Maybe it can be used as a starting point for this, if others think
it makes sense.

The "#ifdef notyet" in the patch would become something like:
# if __FreeBSD_version >= NNNN
when a change to add if_hw_tsomaxseg is done, was what I was
thinking.

rick

> 
> 
> -a
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