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From: Quentin Perret <qperret@google.com>
To: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Marc Zyngier <maz@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Qais Yousef <qais.yousef@arm.com>,
	Suren Baghdasaryan <surenb@google.com>, Tejun Heo <tj@kernel.org>,
	Li Zefan <lizefan@huawei.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	kernel-team@android.com
Subject: Re: [PATCH v6 13/21] sched: Admit forcefully-affined tasks into SCHED_DEADLINE
Date: Tue, 18 May 2021 10:20:38 +0000	[thread overview]
Message-ID: <YKOU9onXUxVLPGaB@google.com> (raw)
In-Reply-To: <20210518094725.7701-14-will@kernel.org>

On Tuesday 18 May 2021 at 10:47:17 (+0100), Will Deacon wrote:
> On asymmetric systems where the affinity of a task is restricted to
> contain only the CPUs capable of running it, admission to the deadline
> scheduler is likely to fail because the span of the sched domain
> contains incompatible CPUs. Although this is arguably the right thing to
> do, it is inconsistent with the case where the affinity of a task is
> restricted after already having been admitted to the deadline scheduler.
> 
> For example, on an arm64 system where not all CPUs support 32-bit
> applications, a 64-bit deadline task can exec() a 32-bit image and have
> its affinity forcefully restricted.

So I guess the alternative would be to fail exec-ing into 32bit from a
64bit DL task, and then drop this patch?

The nice thing about your approach is that existing applications won't
really notice a difference (execve would still 'work'), but on the cons
side it breaks admission control, which is sad.

I don't expect this weird execve-to-32bit pattern from DL to be that
common in practice (at the very least not in Android), so maybe we could
start with the stricter version (fail the execve), and wait to see if
folks complain? Making things stricter later will be harder.

Thoughts?

Thanks,
Quentin

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  reply	other threads:[~2021-05-18 10:27 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 [this message]
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
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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