[Bloat] Phoronix: Linux 5.9 to allow FQ_PIE as default

[Bloat] Phoronix: Linux 5.9 to allow FQ_PIE as default

[Rich Brown]

Is there any "there" here?

https://www.phoronix.com/forums/forum/phoronix/latest-phoronix-articles/1193738-linux-5-9-to-allow-defaulting-to-fq-pie-queuing-discipline-for-fighting-bufferbloat

Thanks.

Re: [Bloat] Phoronix: Linux 5.9 to allow FQ_PIE as default

[Toke Høiland-Jørgensen]

Rich Brown <richb.hanover@gmail.com> writes:

> Is there any "there" here?

I'm sorry, what? :)

> https://www.phoronix.com/forums/forum/phoronix/latest-phoronix-articles/1193738-linux-5-9-to-allow-defaulting-to-fq-pie-queuing-discipline-for-fighting-bufferbloat

As far as the patch, allowing fq_pie as default makes sense in that it
is a "works with defaults" type of qdisc. Which as also the reason used
in the patch IIRC.

Not sure why anyone would *want* to run it as default over fq_codel; but
TBH I have never tried it either, so... *shrugs* :)

-Toke

Re: [Bloat] Phoronix: Linux 5.9 to allow FQ_PIE as default

[Rich Brown]

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I was asking whether there was anything "there" (that is, interesting) in that Phoronix posting / Linux announcement.

> On Jul 15, 2020, at 9:02 AM, Toke Høiland-Jørgensen <toke@toke.dk> wrote:
> 
>> Is there any "there" here?
> 
> I'm sorry, what? :)

Sorry, this is a reference to Gertrude Stein's quote... See Wiktionary - https://en.wiktionary.org/wiki/there_is_no_there_there

Rich

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Re: [Bloat] Phoronix: Linux 5.9 to allow FQ_PIE as default

[Toke Høiland-Jørgensen]

Rich Brown <richb.hanover@gmail.com> writes:

> I was asking whether there was anything "there" (that is, interesting)
> in that Phoronix posting / Linux announcement.

Ah. No, as I said, not really; the patch just added fq_pie to the list
of qdiscs that can be set as default via sysctl...

>> On Jul 15, 2020, at 9:02 AM, Toke Høiland-Jørgensen <toke@toke.dk> wrote:
>> 
>>> Is there any "there" here?
>> 
>> I'm sorry, what? :)
>
> Sorry, this is a reference to Gertrude Stein's quote... See Wiktionary
> - https://en.wiktionary.org/wiki/there_is_no_there_there

Ah, right, not familiar with that :)

-Toke

Re: [Bloat] Phoronix: Linux 5.9 to allow FQ_PIE as default

[Michael Yartys]

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Are there any major differences between fq_codel and fq_pie in terms of their performance? And how does the improved fq_codel called cobalt, which is used in cake, stack up?

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Re: [Bloat] Phoronix: Linux 5.9 to allow FQ_PIE as default

[Jonathan Morton]

> 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

Re: [Bloat] Phoronix: Linux 5.9 to allow FQ_PIE as default

[Toke Høiland-Jørgensen]

Jonathan Morton <chromatix99@gmail.com> writes:

> 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.

No, it isn't - not at compile time. Which is what the phoronix post
references. It's literally this commit:
https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=b97e9d9d67c88bc413a3c27734d45d98d8d52b00

-Toke