From: Juri Lelli <email@example.com> To: Will Deacon <firstname.lastname@example.org> Cc: Daniel Bristot de Oliveira <email@example.com>, Quentin Perret <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, email@example.com, Catalin Marinas <firstname.lastname@example.org>, Marc Zyngier <email@example.com>, Greg Kroah-Hartman <firstname.lastname@example.org>, Peter Zijlstra <email@example.com>, Morten Rasmussen <firstname.lastname@example.org>, Qais Yousef <email@example.com>, Suren Baghdasaryan <firstname.lastname@example.org>, Tejun Heo <email@example.com>, Johannes Weiner <firstname.lastname@example.org>, Ingo Molnar <email@example.com>, Vincent Guittot <firstname.lastname@example.org>, "Rafael J. Wysocki" <email@example.com>, firstname.lastname@example.org Subject: Re: [PATCH v6 13/21] sched: Admit forcefully-affined tasks into SCHED_DEADLINE Date: Fri, 21 May 2021 07:25:51 +0200 [thread overview] Message-ID: <YKdEX9uaQXy8g/Semail@example.com> (raw) In-Reply-To: <20210520180138.GA10523@willie-the-truck> On 20/05/21 19:01, Will Deacon wrote: > On Thu, May 20, 2021 at 02:38:55PM +0200, Daniel Bristot de Oliveira wrote: > > On 5/20/21 12:33 PM, Quentin Perret wrote: > > > On Thursday 20 May 2021 at 11:16:41 (+0100), Will Deacon wrote: > > >> 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?). > > > > > > Still not sure that we can let execve go through ... It will break AC > > > all the same, so it should probably fail as well if AC is on IMO > > > > > > > If the cpumask of the 32-bit task is != of the 64-bit task that is executing it, > > the admission control needs to be re-executed, and it could fail. So I see this > > operation equivalent to sched_setaffinity(). This will likely be true for future > > schedulers that will allow arbitrary affinities (AC should run on affinity > > change, and could fail). > > > > I would vote with Juri: "I'd go with fail hard if AC is on, let it > > pass if AC is off (supposedly the user knows what to do)," (also hope nobody > > complains until we add better support for affinity, and use this as a motivation > > to get back on this front). > > I can have a go at implementing it, but I don't think it's a great solution > and here's why: > > Failing an execve() is _very_ likely to be fatal to the application. It's > also very likely that the task calling execve() doesn't know whether the > program it's trying to execute is 32-bit or not. Consequently, if we go > with failing execve() then all that will happen is that people will disable > admission control altogether. That has a negative impact on "pure" 64-bit > applications and so I think we end up with the tail wagging the dog because > admission control will be disabled for everybody just because there is a > handful of 32-bit programs which may get executed. I understand that it > also means that RT throttling would be disabled. Completely understand your perplexity. But how can the kernel still give guarantees to "pure" 64-bit applications if there are 32-bit applications around that essentially broke admission control when they were restricted to a subset of cores? > Allowing the execve() to continue with a warning is very similar to the > case in which all the 64-bit CPUs are hot-unplugged at the point of > execve(), and this is much closer to the illusion that this patch series > intends to provide. So, for hotplug we currently have a check that would make hotplug operations fail if removing a CPU would mean not enough bandwidth to run the currently admitted set of DEADLINE tasks. > So, personally speaking, I would prefer the behaviour where we refuse to > admit 32-bit tasks vioa sched_set_attr() if the root domain contains > 64-bit CPUs, but we _don't_ fail execve() of a 32-bit program from a > 64-bit deadline task. OK, this is interesting and I guess a very valid alternative. That would force users to create exclusive domains for 32-bit tasks, right? > However, you're the deadline experts so ultimately I'll implement what > you prefer. I just wanted to explain why I think it's a poor interface. > > Have I changed anybody's mind? Partly! :) Thanks a lot for the discussion so far. Juri _______________________________________________ linux-arm-kernel mailing list firstname.lastname@example.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-05-21 5:28 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 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 [this message] 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
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=YKdEX9uaQXy8g/Semail@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --subject='Re: [PATCH v6 13/21] sched: Admit forcefully-affined tasks into SCHED_DEADLINE' \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).