Messages in this thread | | | Date | Sat, 25 Mar 2023 06:42:43 +0100 | Subject | Re: [PATCH net-next] net/core: add optional threading for backlog processing | From | Felix Fietkau <> |
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On 25.03.23 04:19, Jakub Kicinski wrote: > On Fri, 24 Mar 2023 18:57:03 +0100 Felix Fietkau wrote: >> >> 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 >> > >> > Can you give an example? >> > >> > With the 4 CPU example, in case 2 queues are very busy - you're trying >> > to make sure that the RPS does not end up landing on the same CPU as >> > the other busy queue? >> >> In this part I'm thinking about bigger systems where you want to have a >> group of CPUs dedicated to dealing with network traffic without >> assigning a fixed function (e.g. NAPI processing or RPS target) to each >> one, allowing for more dynamic processing. > > I tried the threaded NAPI on larger systems and helped others try, > and so far it's not been beneficial :( Even the load balancing > improvements are not significant enough to use it, and there > is a large risk of scheduler making the wrong decision. > > Hence my questioning - I'm trying to understand what you're doing > differently. I didn't actually run any tests on bigger systems myself, so I don't know how to tune it for those.
>> >> to them and allow the scheduler to take care of the rest. >> > >> > You trust the scheduler much more than I do, I think :) >> >> In my tests it brings down latency (both avg and p99) considerably in >> some cases. I posted some numbers here: >> https://lore.kernel.org/netdev/e317d5bc-cc26-8b1b-ca4b-66b5328683c4@nbd.name/ > > Could you provide the full configuration for this test? > In non-threaded mode the RPS is enabled to spread over remaining > 3 cores? In this test I'm using threaded NAPI and backlog_threaded without any fixed core assignment.
- Felix
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