From: Juri Lelli <juri.lelli@redhat.com>
To: Quentin Perret <qperret@google.com>
Cc: Will Deacon <will@kernel.org>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
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>,
Johannes Weiner <hannes@cmpxchg.org>,
Ingo Molnar <mingo@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: Fri, 21 May 2021 10:39:32 +0200 [thread overview]
Message-ID: <YKdxxDfu81W28n1A@localhost.localdomain> (raw)
In-Reply-To: <YKdsOBCjASzFSzLm@google.com>
On 21/05/21 08:15, Quentin Perret wrote:
> On Friday 21 May 2021 at 07:25:51 (+0200), Juri Lelli wrote:
> > 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.
>
> Right, but only on these dumb 32bit asymmetric systems, and only if we
> care about running 32bits deadline tasks -- which I seriously doubt for
> the Android use-case.
>
> Note that running deadline tasks is also a privileged operation, it
> can't be done by random apps.
>
> > > 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.
>
> Aha, wasn't aware. Any pointers to that check for my education?
Hotplug ends up calling dl_cpu_busy() (after the cpu being hotplugged out
got removed), IIRC. So, if that fails the operation in undone.
> > > 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?
>
> FWIW this is not practical at all for our use-cases, the implications of
> splitting the system in independent root-domains are way too important
> for us to be able to recommend that. Disabling AC, OTOH, sounds simple
> enough. The RT throttling part is the only 'worrying' part, but even
> that may not be the end of the world.
Note that RT throttling (SCHED_{FIFO,RR}) is not handled by DEADLINE
servers yet.
Best,
Juri
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-05-21 8:41 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
2021-05-21 8:15 ` Quentin Perret
2021-05-21 8:39 ` Juri Lelli [this message]
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=YKdxxDfu81W28n1A@localhost.localdomain \
--to=juri.lelli@redhat.com \
--cc=bristot@redhat.com \
--cc=catalin.marinas@arm.com \
--cc=gregkh@linuxfoundation.org \
--cc=hannes@cmpxchg.org \
--cc=kernel-team@android.com \
--cc=linux-arch@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=maz@kernel.org \
--cc=mingo@redhat.com \
--cc=morten.rasmussen@arm.com \
--cc=peterz@infradead.org \
--cc=qais.yousef@arm.com \
--cc=qperret@google.com \
--cc=rjw@rjwysocki.net \
--cc=surenb@google.com \
--cc=tj@kernel.org \
--cc=vincent.guittot@linaro.org \
--cc=will@kernel.org \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).