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From: Rik van Riel <riel@surriel.com>
To: Tejun Heo <tj@kernel.org>, Peter Zijlstra <peterz@infradead.org>
Cc: torvalds@linux-foundation.org, mingo@redhat.com,
	juri.lelli@redhat.com, vincent.guittot@linaro.org,
	dietmar.eggemann@arm.com, rostedt@goodmis.org,
	bsegall@google.com, mgorman@suse.de, bristot@redhat.com,
	vschneid@redhat.com, ast@kernel.org, daniel@iogearbox.net,
	andrii@kernel.org, martin.lau@kernel.org, joshdon@google.com,
	brho@google.com, pjt@google.com, derkling@google.com,
	haoluo@google.com, dvernet@meta.com, dschatzberg@meta.com,
	dskarlat@cs.cmu.edu, linux-kernel@vger.kernel.org,
	bpf@vger.kernel.org, kernel-team@meta.com
Subject: Re: [PATCH 14/31] sched_ext: Implement BPF extensible scheduler class
Date: Tue, 13 Dec 2022 13:40:40 -0500	[thread overview]
Message-ID: <52c9d084d9852cc7c769dbb76f03a13df014c37f.camel@surriel.com> (raw)
In-Reply-To: <Y5jAc/Gs4gVRzkDe@slm.duckdns.org>

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On Tue, 2022-12-13 at 08:12 -1000, Tejun Heo wrote:
> Hello,
> 
> On Tue, Dec 13, 2022 at 11:55:10AM +0100, Peter Zijlstra wrote:
> > On Mon, Dec 12, 2022 at 11:33:12AM -1000, Tejun Heo wrote:
> > 
> > > Here, the way it's handled is a bit different, SCX has
> > > a watchdog mechanism implemented in "[PATCH 18/31] sched_ext:
> > > Implement
> > > runnable task stall watchdog", so if SCX tasks hang for whatever
> > > reason
> > > including being starved by CFS, it will get aborted and all tasks
> > > will be
> > > handed back to CFS. IOW, it's treated like any other BPF
> > > scheduler errors
> > > that can lead to stalls and recovered the same way.
> > 
> > That all sounds quite terrible.. :/
> 
> The main source of difference is that we can't implicitly trust the
> BPF
> scheduler and if it malfunctions or on user request, the system
> should
> always be recoverable, so there are some extra things which are
> inherently
> necessary to support that.
> 
That makes me wonder whether loading an SCX policy
should just have that policy take over all of the
SCHED_OTHER tasks by default, and have a failure of
the policy just return those tasks to CFS?

Having the two be operative at the same time seems
to be a cause of hard to resolve issues, while simply
running all non-RT tasks under the loadable policy
could simplify both internal kernel interfaces, as
well as externally visible effects?

-- 
All Rights Reversed.

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  reply	other threads:[~2022-12-13 18:48 UTC|newest]

Thread overview: 91+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-30  8:22 [PATCHSET RFC] sched: Implement BPF extensible scheduler class Tejun Heo
2022-11-30  8:22 ` [PATCH 01/31] rhashtable: Allow rhashtable to be used from irq-safe contexts Tejun Heo
2022-11-30 16:35   ` Linus Torvalds
2022-11-30 17:00     ` Tejun Heo
2022-12-06 21:36   ` [PATCH v2 " Tejun Heo
2022-12-09 10:50     ` patchwork-bot+netdevbpf
2022-11-30  8:22 ` [PATCH 02/31] cgroup: Implement cgroup_show_cftypes() Tejun Heo
2022-11-30  8:22 ` [PATCH 03/31] BPF: Add @prog to bpf_struct_ops->check_member() Tejun Heo
2022-11-30  8:22 ` [PATCH 04/31] sched: Allow sched_cgroup_fork() to fail and introduce sched_cancel_fork() Tejun Heo
2022-12-12 11:13   ` Peter Zijlstra
2022-12-12 18:03     ` Tejun Heo
2022-12-12 20:07       ` Peter Zijlstra
2022-12-12 20:12         ` Tejun Heo
2022-11-30  8:22 ` [PATCH 05/31] sched: Add sched_class->reweight_task() Tejun Heo
2022-12-12 11:22   ` Peter Zijlstra
2022-12-12 17:34     ` Tejun Heo
2022-12-12 20:11       ` Peter Zijlstra
2022-12-12 20:15         ` Tejun Heo
2022-11-30  8:22 ` [PATCH 06/31] sched: Add sched_class->switching_to() and expose check_class_changing/changed() Tejun Heo
2022-12-12 11:28   ` Peter Zijlstra
2022-12-12 17:59     ` Tejun Heo
2022-11-30  8:22 ` [PATCH 07/31] sched: Factor out cgroup weight conversion functions Tejun Heo
2022-11-30  8:22 ` [PATCH 08/31] sched: Expose css_tg() and __setscheduler_prio() in kernel/sched/sched.h Tejun Heo
2022-12-12 11:49   ` Peter Zijlstra
2022-12-12 17:47     ` Tejun Heo
2022-11-30  8:22 ` [PATCH 09/31] sched: Enumerate CPU cgroup file types Tejun Heo
2022-11-30  8:22 ` [PATCH 10/31] sched: Add @reason to sched_class->rq_{on|off}line() Tejun Heo
2022-12-12 11:57   ` Peter Zijlstra
2022-12-12 18:06     ` Tejun Heo
2022-11-30  8:22 ` [PATCH 11/31] sched: Add @reason to sched_move_task() Tejun Heo
2022-12-12 12:00   ` Peter Zijlstra
2022-12-12 17:54     ` Tejun Heo
2022-11-30  8:22 ` [PATCH 12/31] sched: Add normal_policy() Tejun Heo
2022-11-30  8:22 ` [PATCH 13/31] sched_ext: Add boilerplate for extensible scheduler class Tejun Heo
2022-11-30  8:22 ` [PATCH 15/31] sched_ext: [TEMPORARY] Add temporary workaround kfunc helpers Tejun Heo
2022-11-30  8:22 ` [PATCH 16/31] sched_ext: Add scx_example_dummy and scx_example_qmap example schedulers Tejun Heo
2022-11-30  8:22 ` [PATCH 17/31] sched_ext: Add sysrq-S which disables the BPF scheduler Tejun Heo
2022-11-30  8:23 ` [PATCH 18/31] sched_ext: Implement runnable task stall watchdog Tejun Heo
2022-11-30  8:23 ` [PATCH 19/31] sched_ext: Allow BPF schedulers to disallow specific tasks from joining SCHED_EXT Tejun Heo
2022-11-30  8:23 ` [PATCH 20/31] sched_ext: Allow BPF schedulers to switch all eligible tasks into sched_ext Tejun Heo
2022-11-30  8:23 ` [PATCH 21/31] sched_ext: Implement scx_bpf_kick_cpu() and task preemption support Tejun Heo
2022-11-30  8:23 ` [PATCH 22/31] sched_ext: Add task state tracking operations Tejun Heo
2022-11-30  8:23 ` [PATCH 23/31] sched_ext: Implement tickless support Tejun Heo
2022-11-30  8:23 ` [PATCH 24/31] sched_ext: Add cgroup support Tejun Heo
2022-11-30  8:23 ` [PATCH 25/31] sched_ext: Implement SCX_KICK_WAIT Tejun Heo
2022-11-30  8:23 ` [PATCH 26/31] sched_ext: Implement sched_ext_ops.cpu_acquire/release() Tejun Heo
2022-11-30  8:23 ` [PATCH 27/31] sched_ext: Implement sched_ext_ops.cpu_online/offline() Tejun Heo
2022-11-30  8:23 ` [PATCH 28/31] sched_ext: Add Documentation/scheduler/sched-ext.rst Tejun Heo
2022-12-12  4:01   ` Bagas Sanjaya
2022-12-12  6:28     ` Tejun Heo
2022-12-12 13:07       ` Bagas Sanjaya
2022-12-12 17:30         ` Tejun Heo
2022-12-12 12:39   ` Peter Zijlstra
2022-12-12 17:16     ` Tejun Heo
2022-11-30  8:23 ` [PATCH 29/31] sched_ext: Add a basic, userland vruntime scheduler Tejun Heo
2022-11-30  8:23 ` [PATCH 30/31] BPF: [TEMPORARY] Nerf BTF scalar value check Tejun Heo
2022-11-30  8:23 ` [PATCH 31/31] sched_ext: Add a rust userspace hybrid example scheduler Tejun Heo
2022-12-12 14:03   ` Peter Zijlstra
2022-12-12 21:05     ` Peter Oskolkov
2022-12-13 11:02       ` Peter Zijlstra
2022-12-13 18:24         ` Peter Oskolkov
2022-12-12 22:00     ` Tejun Heo
2022-12-12 22:18     ` Josh Don
2022-12-13 11:30       ` Peter Zijlstra
2022-12-13 20:33         ` Tejun Heo
2022-12-14  2:00         ` Josh Don
     [not found] ` <20221130082313.3241517-15-tj@kernel.org>
2022-12-02 17:08   ` [PATCH 14/31] sched_ext: Implement BPF extensible scheduler class Barret Rhoden
2022-12-02 18:01     ` Tejun Heo
2022-12-06 21:42       ` Tejun Heo
2022-12-06 21:44   ` Tejun Heo
2022-12-11 22:33   ` Julia Lawall
2022-12-12  2:15     ` Tejun Heo
2022-12-12  6:03       ` Julia Lawall
2022-12-12  6:08         ` Tejun Heo
2022-12-12 12:31   ` Peter Zijlstra
2022-12-12 20:03     ` Tejun Heo
2022-12-12 12:53   ` Peter Zijlstra
2022-12-12 21:33     ` Tejun Heo
2022-12-13 10:55       ` Peter Zijlstra
2022-12-13 18:12         ` Tejun Heo
2022-12-13 18:40           ` Rik van Riel [this message]
2022-12-13 23:20             ` Josh Don
2022-12-13 10:57       ` Peter Zijlstra
2022-12-13 17:32         ` Tejun Heo
2022-12-12  9:37 ` [PATCHSET RFC] sched: " Peter Zijlstra
2022-12-12 17:27   ` Tejun Heo
2022-12-12 10:14 ` Peter Zijlstra
2022-12-14  2:11   ` Josh Don
2022-12-14  8:55     ` Peter Zijlstra
2022-12-14 22:23       ` Tejun Heo
2022-12-14 23:20         ` Barret Rhoden

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