[Cake] Cake - flow (or host) weight request - how to implement

[Cake] Cake - flow (or host) weight request - how to implement

[Jan Rovner]

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Hello,

I am trying to experiment with sch_cake.c, my goal is to ad-hoc prioritize / deprioritize traffic served to specified a host(s). The prioritization would be controlled by an external system and it should handle well the situation where a host has active flow(s).

I've experimented with traffic shifting from tin to tin via fwmarks, it worked somehow, but there are issues related to losing flow's (cobalt) state.

Could you please propose a way how this could be done?

Each flow refences cake_host_table, which could be in theory modified (for example) like

struct cake_host {
    u32 srchost_tag;
    u32 dsthost_tag;
    u16 srchost_bulk_flow_count;
    u16 dsthost_bulk_flow_count;

    ??? srchost_weight;  // default value = 1.0
    ??? dsthost_weight;  // default value = 1.0
};

The weight fields could be then used in cobalt rate scheduling... weight could be an integer, enum, or decimal - but anything that could distinguish the traffic.

Thank you for any ideas.


Jan Rovner
Ing. Jan Rovner, Ph.D., jednatel společnosti

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Re: [Cake] Cake - flow (or host) weight request - how to implement

[Stephen Hemminger]

On Wed, 27 Sep 2023 17:48:06 +0000
Jan Rovner via Cake <cake@lists.bufferbloat.net> wrote:

> Hello,
> 
> I am trying to experiment with sch_cake.c, my goal is to ad-hoc prioritize / deprioritize traffic served to specified a host(s). The prioritization would be controlled by an external system and it should handle well the situation where a host has active flow(s).

Is it possible to use one or more existing BPF hooks to change DCSP bits for that paths you wish to adjust.
The point is that changes to upstream base code are hard to maintain, and that is what BPF initial hooks
were meant to provide.

Re: [Cake] Cake - flow (or host) weight request - how to implement

[Sebastian Moeller]

Hi Stephen,




> On Sep 27, 2023, at 22:27, Stephen Hemminger via Cake <cake@lists.bufferbloat.net> wrote:
> 
> On Wed, 27 Sep 2023 17:48:06 +0000
> Jan Rovner via Cake <cake@lists.bufferbloat.net> wrote:
> 
>> Hello,
>> 
>> I am trying to experiment with sch_cake.c, my goal is to ad-hoc prioritize / deprioritize traffic served to specified a host(s). The prioritization would be controlled by an external system and it should handle well the situation where a host has active flow(s).
> 
> Is it possible to use one or more existing BPF hooks to change DCSP bits for that paths you wish to adjust.
> The point is that changes to upstream base code are hard to maintain, and that is what BPF initial hooks
> were meant to provide.

	IIUC the OP wants not only to steer packets into a specific tier but really wants to move a hash-bins complete state between tiers (he talks about cobalt state). My (limited) understanding is that this would need changes to cake's kernel code, either by always keeping shadow cobalt state per hash-bin in all tiers or by implementing a state copy procedure...
	Now, I am not sure how well moving flows around priority tiers is going to work on a timescale that preserving the cobalt state seems important and how to avoid re-ordering if a a flow is increased in priority while it still has queued packets in the lower priority tier (maybe the solution is moving both cobalt state and queued packets between tiers).

Regards
	Sebastian



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