Messages in this thread | | | Date | Tue, 21 Apr 2020 15:28:23 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH 0/4] sched/rt: Distribute tasks in find_lowest_rq() |
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On 2020-04-21 15:22, Qais Yousef wrote: > On 04/21/20 15:09, Marc Zyngier wrote: >> On 2020-04-21 14:18, Valentin Schneider wrote: >> > On 21/04/20 13:13, Qais Yousef wrote: >> >> [...] >> >> > > I CCed Marc who's the maintainer of this file who can clarify better >> > > if this >> > > really breaks anything. >> > > >> > > If any interrupt expects to be affined to a specific CPU then this >> > > must be >> > > described in DT/driver. I think the GIC controller is free to >> > > distribute them >> > > to any cpu otherwise if !force. Which is usually done by >> > > irq_balancer anyway >> > > in userspace, IIUC. >> > > >> > > I don't see how cpumask_any_and() break anything here too. I >> > > actually think it >> > > improves on things by better distribute the irqs on the system by >> > > default. >> >> That's a pretty bold statement. Unfortunately, it isn't universally >> true. >> Some workload will be very happy with interrupts spread all over the >> map, >> and some others will suffer from it because, well, it interrupts >> userspace. >> >> > As you say, if someone wants smarter IRQ affinity they can do >> > irq_balancer >> > and whatnot. The default kernel policy for now has been to shove >> > everything >> > on the lowest-numbered CPU, and I see no valid reason to change that. >> >> Exactly. I would like to keep the kernel policy as simple as possible >> for >> non-managed interrupts (managed interrupts are another kettle of fish >> entirely). >> Userpace is in control to place things "intelligently", so let's not >> try and >> make the kernel smarter than it strictly needs to be. > > Fair enough. But why is it asking for cpumask_any() in the first place?
Implementation detail. Turn it into cpumask_first_and() if you want.
M. -- Jazz is not dead. It just smells funny...
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