From: Will Deacon <email@example.com> To: Juri Lelli <firstname.lastname@example.org> Cc: Quentin Perret <email@example.com>, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, Catalin Marinas <email@example.com>, Marc Zyngier <firstname.lastname@example.org>, Greg Kroah-Hartman <email@example.com>, Peter Zijlstra <firstname.lastname@example.org>, Morten Rasmussen <email@example.com>, Qais Yousef <firstname.lastname@example.org>, Suren Baghdasaryan <email@example.com>, Tejun Heo <firstname.lastname@example.org>, Johannes Weiner <email@example.com>, Ingo Molnar <firstname.lastname@example.org>, Vincent Guittot <email@example.com>, "Rafael J. Wysocki" <firstname.lastname@example.org>, email@example.com, Daniel Bristot de Oliveira <firstname.lastname@example.org> Subject: Re: [PATCH v6 13/21] sched: Admit forcefully-affined tasks into SCHED_DEADLINE Date: Thu, 20 May 2021 11:16:41 +0100 [thread overview] Message-ID: <20210520101640.GA10065@willie-the-truck> (raw) In-Reply-To: <YKYoQ0ezahSC/RAg@localhost.localdomain> Hi Juri, On Thu, May 20, 2021 at 11:13:39AM +0200, Juri Lelli wrote: > Apologies for the delay in replying. Not at all! > On 18/05/21 13:19, Quentin Perret wrote: > > On Tuesday 18 May 2021 at 11:59:51 (+0100), Will Deacon wrote: > > > On Tue, May 18, 2021 at 10:48:07AM +0000, Quentin Perret wrote: > > > > On Tuesday 18 May 2021 at 11:28:34 (+0100), Will Deacon wrote: > > > > > I don't have strong opinions on this, but I _do_ want the admission via > > > > > sched_setattr() to be consistent with execve(). What you're suggesting > > > > > ticks that box, but how many applications are prepared to handle a failed > > > > > execve()? I suspect it will be fatal. > > > > > > > > Yep, probably. > > > > > > > > > Probably also worth pointing out that the approach here will at least > > > > > warn in the execve() case when the affinity is overridden for a deadline > > > > > task. > > > > > > > > Right so I think either way will be imperfect, so I agree with the > > > > above. > > > > > > > > Maybe one thing though is that, IIRC, userspace _can_ disable admission > > > > control if it wants to. In this case I'd have no problem with allowing > > > > this weird behaviour when admission control is off -- the kernel won't > > > > provide any guarantees. But if it's left on, then it's a different > > > > story. > > > > > > > > So what about we say, if admission control is off, we allow execve() and > > > > sched_setattr() with appropriate warnings as you suggest, but if > > > > admission control is on then we fail both? > > > > > > That's an interesting idea. The part that I'm not super keen about is > > > that it means admission control _also_ has an effect on the behaviour of > > > execve() > > > > Right, that's a good point. And it looks like fork() behaves the same > > regardless of admission control being enabled or not -- it is forbidden > > from DL either way. So I can't say there is a precedent :/ > > > > > so practically you'd have to have it disabled as long as you > > > have the possibility of 32-bit deadline tasks anywhere in the system, > > > which impacts 64-bit tasks which may well want admission control enabled. > > > > Indeed, this is a bit sad, but I don't know if the kernel should pretend > > it can guarantee to meet your deadlines and at the same time allow to do > > something that wrecks the underlying theory. > > > > I'd personally be happy with saying that admission control should be > > disabled on these dumb systems (and have that documented), at least > > until DL gets proper support for affinities. ISTR there was work going > > in that direction, but some folks in the CC list will know better. > > > > @Juri, maybe you would know if that's still planned? > > I won't go as far as saying planned, but that is still under "our" radar > for sure. Daniel was working on it, but I don't think he had any time to > resume that bit of work lately. > > So, until we have that, I think we have been as conservative as we could > for this type of decisions. I'm a little afraid that allowing > configuration to break admission control (even with a non fatal warning > is emitted) is still risky. I'd go with fail hard if AC is on, let it > pass if AC is off (supposedly the user knows what to do). But I'm not > familiar with the mixed 32/64 apps usecase you describe, so I might be > missing details. Ok, thanks for the insight. In which case, I'll go with what we discussed: require admission control to be disabled for sched_setattr() but allow execve() to a 32-bit task from a 64-bit deadline task with a warning (this is probably similar to CPU hotplug?). I'll update that for v8, and this patch will disappear. Will _______________________________________________ linux-arm-kernel mailing list email@example.com http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-05-20 10:18 UTC|newest] Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-05-18 9:47 [PATCH v6 00/21] Add support for 32-bit tasks on asymmetric AArch32 systems Will Deacon 2021-05-18 9:47 ` [PATCH v6 01/21] arm64: cpuinfo: Split AArch32 registers out into a separate struct Will Deacon 2021-05-21 10:47 ` Catalin Marinas 2021-05-18 9:47 ` [PATCH v6 02/21] arm64: Allow mismatched 32-bit EL0 support Will Deacon 2021-05-21 10:25 ` Catalin Marinas 2021-05-24 12:05 ` Will Deacon 2021-05-24 13:49 ` Catalin Marinas 2021-05-21 10:41 ` Catalin Marinas 2021-05-24 12:09 ` Will Deacon 2021-05-24 13:46 ` Catalin Marinas 2021-05-21 15:22 ` Qais Yousef 2021-05-24 20:21 ` Will Deacon 2021-05-18 9:47 ` [PATCH v6 03/21] KVM: arm64: Kill 32-bit vCPUs on systems with mismatched " Will Deacon 2021-05-21 10:47 ` Catalin Marinas 2021-05-18 9:47 ` [PATCH v6 04/21] arm64: Kill 32-bit applications scheduled on 64-bit-only CPUs Will Deacon 2021-05-21 10:55 ` Catalin Marinas 2021-05-18 9:47 ` [PATCH v6 05/21] arm64: Advertise CPUs capable of running 32-bit applications in sysfs Will Deacon 2021-05-21 11:00 ` Catalin Marinas 2021-05-18 9:47 ` [PATCH v6 06/21] sched: Introduce task_cpu_possible_mask() to limit fallback rq selection Will Deacon 2021-05-21 16:03 ` Peter Zijlstra 2021-05-24 12:17 ` Will Deacon 2021-05-18 9:47 ` [PATCH v6 07/21] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1 Will Deacon 2021-05-21 17:39 ` Qais Yousef 2021-05-24 20:21 ` Will Deacon 2021-05-18 9:47 ` [PATCH v6 08/21] cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus() Will Deacon 2021-05-21 16:25 ` Qais Yousef 2021-05-24 21:09 ` Will Deacon 2021-05-18 9:47 ` [PATCH v6 09/21] sched: Reject CPU affinity changes based on task_cpu_possible_mask() Will Deacon 2021-05-18 9:47 ` [PATCH v6 10/21] sched: Introduce task_struct::user_cpus_ptr to track requested affinity Will Deacon 2021-05-18 9:47 ` [PATCH v6 11/21] sched: Split the guts of sched_setaffinity() into a helper function Will Deacon 2021-05-21 16:41 ` Qais Yousef 2021-05-24 21:16 ` Will Deacon 2021-05-18 9:47 ` [PATCH v6 12/21] sched: Allow task CPU affinity to be restricted on asymmetric systems Will Deacon 2021-05-21 17:11 ` Qais Yousef 2021-05-24 21:43 ` Will Deacon 2021-05-18 9:47 ` [PATCH v6 13/21] sched: Admit forcefully-affined tasks into SCHED_DEADLINE Will Deacon 2021-05-18 10:20 ` Quentin Perret 2021-05-18 10:28 ` Will Deacon 2021-05-18 10:48 ` Quentin Perret 2021-05-18 10:59 ` Will Deacon 2021-05-18 13:19 ` Quentin Perret 2021-05-20 9:13 ` Juri Lelli 2021-05-20 10:16 ` Will Deacon [this message] 2021-05-20 10:33 ` Quentin Perret 2021-05-20 12:38 ` Juri Lelli 2021-05-20 12:38 ` Daniel Bristot de Oliveira 2021-05-20 15:06 ` Dietmar Eggemann 2021-05-20 16:00 ` Daniel Bristot de Oliveira 2021-05-20 17:55 ` Dietmar Eggemann 2021-05-20 18:03 ` Will Deacon 2021-05-21 11:26 ` Dietmar Eggemann 2021-05-20 18:01 ` Will Deacon 2021-05-21 5:25 ` Juri Lelli 2021-05-21 8:15 ` Quentin Perret 2021-05-21 8:39 ` Juri Lelli 2021-05-21 10:37 ` Will Deacon 2021-05-21 11:23 ` Dietmar Eggemann 2021-05-21 13:02 ` Quentin Perret 2021-05-21 14:04 ` Juri Lelli 2021-05-21 17:47 ` Dietmar Eggemann 2021-05-21 13:00 ` Daniel Bristot de Oliveira 2021-05-21 13:12 ` Quentin Perret 2021-05-24 20:47 ` Will Deacon 2021-05-18 9:47 ` [PATCH v6 14/21] freezer: Add frozen_or_skipped() helper function Will Deacon 2021-05-18 9:47 ` [PATCH v6 15/21] sched: Defer wakeup in ttwu() for unschedulable frozen tasks Will Deacon 2021-05-18 9:47 ` [PATCH v6 16/21] arm64: Implement task_cpu_possible_mask() Will Deacon 2021-05-24 14:57 ` Catalin Marinas 2021-05-18 9:47 ` [PATCH v6 17/21] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 Will Deacon 2021-05-24 15:02 ` Catalin Marinas 2021-05-18 9:47 ` [PATCH v6 18/21] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system Will Deacon 2021-05-24 15:46 ` Catalin Marinas 2021-05-24 20:32 ` Will Deacon 2021-05-25 9:43 ` Catalin Marinas 2021-05-18 9:47 ` [PATCH v6 19/21] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0 Will Deacon 2021-05-24 15:47 ` Catalin Marinas 2021-05-18 9:47 ` [PATCH v6 20/21] arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores Will Deacon 2021-05-24 15:47 ` Catalin Marinas 2021-05-18 9:47 ` [PATCH v6 21/21] Documentation: arm64: describe asymmetric 32-bit support Will Deacon 2021-05-21 17:37 ` Qais Yousef 2021-05-24 21:46 ` Will Deacon 2021-05-24 16:22 ` Catalin Marinas 2021-05-21 17:45 ` [PATCH v6 00/21] Add support for 32-bit tasks on asymmetric AArch32 systems Qais Yousef 2021-05-24 22:08 ` Will Deacon
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