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From: Peter Zijlstra <peterz@infradead.org>
To: Tejun Heo <tj@kernel.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, riel@surriel.com,
	linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
	kernel-team@meta.com
Subject: Re: [PATCHSET RFC] sched: Implement BPF extensible scheduler class
Date: Mon, 12 Dec 2022 10:37:50 +0100	[thread overview]
Message-ID: <Y5b2btWFJeEfTyJg@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20221130082313.3241517-1-tj@kernel.org>

On Tue, Nov 29, 2022 at 10:22:42PM -1000, Tejun Heo wrote:

> Core scheduling is an example of a feature that took a significant amount of
> time and effort to integrate into the kernel.

Mostly because I dropped it on the floor once I heard about MDS. That
made me lose interest entirely. The only reason it eventually happened
was ChromeOS (Joel) pushing for it again.

> Part of the difficulty with core
> scheduling was the inherent mismatch in abstraction between the desire to
> perform core-wide scheduling, and the per-cpu design of the kernel scheduler.

Not really; the main difficultly was due to me wanting to do it outside
of the scheduling classes so that it fundamentally covers all of them.

Doing it inside a class (say CFS) would've made it significantly simpler.

> This caused issues, for example ensuring proper fairness between the
> independent runqueues of SMT siblings.

Inter-runqueue fairness is a known issue of CFS and quite independent of
core scheduling.


Anyway, I hate all of this. Linus NAK'ed loadable schedulers a number of
times in the past and this is just that again -- with the extra downside
of the whole BPF thing on top  :/

You look to be exposing a ton of stuff I've so far even refused
tracepoints for :-(

Anyway, I'm just back from a heavy dose of Covid and still taking it
easy, but I'll go read through the whole thing, hopefully I'll finish
before vanishing again for the x-mas break.

  parent reply	other threads:[~2022-12-12  9:38 UTC|newest]

Thread overview: 92+ 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 14/31] sched_ext: Implement BPF " Tejun Heo
2022-12-02 17:08   ` 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
2022-12-13 23:20             ` Josh Don
2022-12-13 10:57       ` Peter Zijlstra
2022-12-13 17:32         ` 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
2022-12-12  9:37 ` Peter Zijlstra [this message]
2022-12-12 17:27   ` [PATCHSET RFC] sched: Implement BPF extensible scheduler class 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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