Re: [Cerowrt-devel] fq_pie for linux

[Dave Taht <dave.taht@gmail.com>]

On Thu, Dec 6, 2018 at 12:13 PM David Lang <david@lang.hm> wrote:
>
> On Thu, 6 Dec 2018, Dave Taht wrote:
>
> > Toke Høiland-Jørgensen <toke@toke.dk> writes:
> >
> >> Dave Taht <dave.taht@gmail.com> writes:
> >>
> >>> https://github.com/gautamramk/FQ-PIE-for-Linux-Kernel/issues/2
> >>
> >> With all the variants of fq+AQM, maybe decoupling the FQ part and the
> >> AQM part would be worthwhile, instead of reimplementing it for each
> >> variant...
> >
> > I actually sat down to write a userspace implementation of the fq bits
> > in C with a pluggable AQM a while back. I called it "drrp".
> >
> > I think that there are many applications today that do too much
> > processing per packet, and end up with their recv socket buffer
> > overflowing (ENOBUFS) and tail-dropping in the kernel. I've certainly
> > seen this with babeld, in particular.
> >
> > So by putting an intervening layer around the udp recv call to keep
> > calling that as fast as possible, and try to FQ and AQM the result, I
> > thought we'd get better fairness between different flows over udp and a
> > smarter means of shedding load when that was happening.
> >
> > Then... there was all this activity recently around other approaches to
> > the udp problem in the kernel, and I gave up while that got sorted out.
>
> one of these is (IIRC) mmreceive, which lets the app get all the pending packets
> from the Linux UDP stack in one systemcall rather than having to make one
> syscall per packet. In rsyslog this is a significant benefit at high packet
> rates.

Are you referring to recvmmsg? That's always been problematic (it
would block), but I keep hoping it's been fixed.

While I'm kvetching about udp and userspace, would love the equivalent
of high and low watermarks to work. select can return when there is
only 1 byte of space available and thus you have to retry until
there's room for a packet.

I'm totally incapable of writing such a thing. I find these bits of
the kernel impenetrable.

>
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-- 

Dave Täht
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