RT/Linux SCHED_RR/_FIXED to combat latency?

[Damien Miller]

On Thu, 10 Aug 2023, Cedric Blancher wrote:

> Good morning!
> 
> We're experiencing rather very bad latency spikes on busy Linux
> systems, for example if one machine is the jumphost (ssh -J) for a few
> hundred connections, while at the same time handles CPU intensive
> tasks.
> 
> Would RT/Linux SCHED_FIXED or SCHED_RR be of help in such a case, e.g.
> put all ssh processes into the SCHED_FIXED scheduling class, with a
> priority higher than the non-interactive compute processes?

If the problem is load caused by the ssh connections then a different
scheduling class isn't likely to help.

> Also, do I interpret it correctly that each forwarded TCP connection
> has its own process?!

Usually yes. If you're using connection multiplexing (ControlPath/
ControlMaster/ControlPersist) then connections from the same user
through the same jump host can be shared.

-d