Hi Peter, On Wed, 3 Sep 2025 22:05:20 +0200 Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: [...] > > Yuri is proposing to ignore dl-servers bandwidth contribution from > > admission control (as they essentially operate on the remaining > > bandwidth portion not available to RT/DEADLINE tasks): > > > > https://lore.kernel.org/lkml/20250903114448.664452-1-yurand2000@xxxxxxxxx/ > > > > His patch should make this patch not required. Would you be able and > > willing to test this assumption? > > > > I don't believe Peter already expressed his opinion on what Yuri is > > proposing, so this might be moot. > > Urgh, yeah, I don't like that at all. That reasoning makes no sense > what so ever. That 5% is not lost time, that 5% is being very > optimistic and 'models' otherwise unaccountable time like IRQ and > random overheads. > > Thinking you can give out 100% CPU time to a bandwidth limited group > of tasks is delusional. > > Explicitly not accounting things that you *can* is just plain wrong. > So no, Yuri's thing is not going to go anywhere. The goal of Yuri's patch was not to avoid accounting things... The goal was to avoid subtracting the fair dl server utilization from the utilization reserved for real-time tasks (assuming that /proc/sys/kernel/sched_rt_runtime_us / /proc/sys/kernel/sched_rt_period_us represents the fraction of CPU time reserved for real-time tasks). Maybe we made errors in describing the patch (or in some details of the implementation), but the final goal was just to ensure that sched_rt_runtime_us/sched_rt_period_us goes to RT tasks; the remaining fraction of CPU time is shared by SCHED_OTHER tasks, fair dl servers, IRQs, and other overhead (the fair dl server utilization can be smaller than 1-sched_rt_runtime_us/sched_rt_period_us, so some time can be explicitly left for IRQs and kernel). Luca Luca
