Messages in this thread | | | Date | Fri, 24 Mar 2023 18:35:00 +0100 | From | Felix Fietkau <> | Subject | Re: [PATCH net-next] net/core: add optional threading for backlog processing |
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On 24.03.23 18:20, Jakub Kicinski wrote: > On Fri, 24 Mar 2023 18:13:14 +0100 Felix Fietkau wrote: >> When dealing with few flows or an imbalance on CPU utilization, static RPS >> CPU assignment can be too inflexible. Add support for enabling threaded NAPI >> for backlog processing in order to allow the scheduler to better balance >> processing. This helps better spread the load across idle CPUs. > > Can you explain the use case a little bit more?
I'm primarily testing this on routers with 2 or 4 CPUs and limited processing power, handling routing/NAT. RPS is typically needed to properly distribute the load across all available CPUs. When there is only a small number of flows that are pushing a lot of traffic, a static RPS assignment often leaves some CPUs idle, whereas others become a bottleneck by being fully loaded. Threaded NAPI reduces this a bit, but CPUs can become bottlenecked and fully loaded by a NAPI thread alone.
Making backlog processing threaded helps split up the processing work even more and distribute it onto remaining idle CPUs.
It can basically be used to make RPS a bit more dynamic and configurable, because you can assign multiple backlog threads to a set of CPUs and selectively steer packets from specific devices / rx queues to them and allow the scheduler to take care of the rest.
- Felix
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