[Cake] CAKE upstreaming - testers wanted, ACK filtering rescuers needed

Toke Høiland-Jørgensen toke at toke.dk
Thu Apr 26 03:34:11 EDT 2018

Kevin Darbyshire-Bryant <kevin at darbyshire-bryant.me.uk> writes:

>> On 25 Apr 2018, at 21:45, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
>> For those who have not been following the discussion on the upstreaming
>> patches, here's an update:
>> <snip>
>> So please do test the current git version (cobalt branch, still). I'm
>> planning to resubmit on Friday.
> The two routers running that latest code survived the night which is a
> good sign.


> I’ve sort of half been following the ‘discussion’, as ever the
> reaction from the kernel people makes it a place I never wish to
> look/contribute, ….. this from Eric has me disturbed "If you keep
> saying this old urban legend, I will NACK your patch.I am tired of
> people pretending GSO/TSO are bad for latencies.”

Heh, yeah, the tone on kernel lists can be a bit... abrasive... just
smile and wave and ignore the vitriol is my approach. But I can totally
understand why some people don't want to put up with it... :)

> Genuine question:  I have a superpacket circa 64K, this is a lump of
> data in a tcp flow.  I have another small VOIP packet, it’s latency
> sensitive.  If I split the super packet into individual 1.5K packets
> as they would be on the wire, I can insert my VOIP packet at suitable
> place in time such that jitter targets are not exceeded.  If I don’t
> split the super packet, surely I have to wait till the end of the
> superpacket’s queue (for want of a better word) and possibly exceed my
> latency target.  That looks to me like ‘GSO/TSO’ is potentially bad
> for interflow latencies.  What don’t I understand here?

You are right in principle, of course. I *think* that what Eric means is
that the GSO logic should automatically size the GSO superpackets so the
latency cost is negligible for the actual link rate. I was actually
thinking I would do some measurements at some point to test this at
various rates; since we have a nice piece of code that can adaptively
split GSO packets that should be pretty straight-forward :)


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