[Bloat] fq_pie in FreeBSD... Re: Phoronix: Linux 5.9 to allow FQ_PIE as default

[grenville armitage <garmitage@swin.edu.au>]

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A tangent for anyone who is running a FreeBSD-based gateway, there's also an fq_pie in dummynet (https://reviews.freebsd.org/rS300779). I haven't played with it for a long time, but still curious if anyone's experimented with that combination. (Particularly if the on-the-wire behavior differs from that of linux fq-pie.)

cheers,
gja

On 2020-07-16 10:37, Jonathan Morton wrote:
> > On 16 Jul, 2020, at 12:58 am, Michael Yartys via Bloat <bloat@lists.bufferbloat.net> wrote:
> >
> > Are there any major differences between fq_codel and fq_pie in terms of their performance?
>
> I think some tests were run some time ago which showed significantly better behaviour by fq_codel than fq_pie. In particular, the latter used only a single AQM instead of an independent one for each flow. I'm not sure whether it's been changed since then.
>
> The only advantage I can see for PIE over Codel is, possibly, a reduction of system load for use of the AQM. But fq_codel is already pretty efficient so that would be an edge case.
>
> In any case, it is already possible to chose any qdisc you like (with default parameters) as the default qdisc. I'm really not sure what the fuss is about.
>
> > And how does the improved fq_codel called cobalt, which is used in cake, stack up?
>
> COBALT has some modifications to basic Codel which, I think, could profitably be backported into fq_codel. It also has a particular extra mode, based on BLUE, for dealing with unresponsive traffic (that continued to build queue even after lots of ECN signalling and/or Cdel-scheduled packet drops). It is the latter which inspired the name.
>
> For the other major functional component of fq_codel, Cake also has a set-associative hash function for allocating flows into queues, which substantially reduces the probability of hash collisions in most cases.
>
> - Jonathan Morton
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