Re: tc packet drop in high priority queue

Linux Advanced Routing and Traffic Control

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> On June 1, 2015 at 6:49 PM "jsullivan@xxxxxxxxxxxxxxxxxxx"
> <jsullivan@xxxxxxxxxxxxxxxxxxx> wrote:
> 
> 
>  > On June 1, 2015 at 6:37 PM Dave Taht <dave.taht@xxxxxxxxx> wrote:
>  >
>  +> > <snip>
>  > > Interesting. We do a lot of video work and hence UDP. For heavily mixed
>  > > environments with high bandwidth and sometimes high latency, is fq_codel
>  > > still
>  > > the preferred leaf qdisc or should we be investigating sch_fq? Thanks -
>  > > John
>  >
>  > The answer is too nuanced to fit into the margins of this email. :)
>  >
>  > I believe FAR more research and development work is needed on low
>  > latency udp or current-ly using udp - applications. Most of the
>  > industry focus is (and has always been) on making tcp perform well -
>  > and me, well, it is obvious that we are going to lose the existing
>  > phone system in under 2 decades - and we need to replace it with a
>  > (hopefully better) internet, add videoconferencing, and make other
>  > highly interactive apps like games co-exist with netflix.
>  >
>  >
>  > But:
>  >
>  > What exactly do you mean by leaf qdisc in this question?
>  >
>  > Latency happens at the bottleneck links to the largest extent, but
>  > there is also latency that accrues within a machine at various layers
>  > in the stack. you need to find and improve the bottlenecks, which is
>  > something of a wackamole exercise.
>  >
>  > My principal concern (today) with the potential wide deployment of
>  > sch_fq (over fq_codel) is
>  > that sch_fq generates a unique internal id per new flow which is not
>  > sufficiently resistant to DDOS attacks for my taste. sch_fq has
>  > "improved" lately with some protection for that, but it disables the
>  > distinct per-flow-fq-advantage sch_fq brought to the party in the
>  > first place, but, (on the gripping hand) may well be the closest thing
>  > to the right thing for your application mix! Try it! report back! :)
>  >
>  > fq_codel is faster and safer in a wider range of environments than
>  > anything else we got. Safety is an important feature...
>  >
>  > Other ideas at the protocol layer for "things with cookies" - would be
>  > nice - like, (the now impossible to implement) rfc6013 - and Quic is
>  > quite promising - these ideas strike me as a long term answer to the
>  > bcp38 and DDOS problem, but those ideas need to move into voip
>  > transactions.
>  ><snip>
  By leaf I mean that we typically use HFSC as our qdisc to shape our latency
very accurately.  We then put fq_codel as the leaf qdisc on its classes.  Thanks
- John
   
 

 
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