From: Tejun Heo <tj@kernel.org>
To: Barret Rhoden <brho@google.com>
Cc: torvalds@linux-foundation.org, mingo@redhat.com,
peterz@infradead.org, 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, 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: [PATCH 14/31] sched_ext: Implement BPF extensible scheduler class
Date: Tue, 6 Dec 2022 11:42:27 -1000 [thread overview]
Message-ID: <Y4+3Q2FnG1bsGH55@slm.duckdns.org> (raw)
In-Reply-To: <Y4o9gV2v8eyI1arK@slm.duckdns.org>
Hello, Barret.
On Fri, Dec 02, 2022 at 08:01:37AM -1000, Tejun Heo wrote:
> > you still end up grabbing both locks, but just not at the same time.
>
> Yeah, this probably would look better than the current double lock dancing,
> especially in the finish_dispatch() path.
>
> > plus, task_rq_lock() takes the guesswork out of whether you're getting p's
> > rq lock or not. it looks like you're using the holding_cpu to handle the
> > race where p moves cpus after you read task_rq(p) but before you lock that
> > task_rq. maybe you can drop the whole concept of the holding_cpu?
>
> ->holding_cpu is there to basically detect intervening dequeues, so if we
> lock them out with TASK_ON_RQ_MIGRATING, we might be able to drop it. I need
> to look into it more tho. Things get pretty subtle around there, so I could
> easily be missing something. I'll try this and let you know how it goes.
I tried both and I'm pretty ambivalent. The problem is that the
finish_dispatch() path can't use TASK_ON_RQ_MIGRATING the way the consume
path does because the dispatch path isn't starting with the task locked. The
only claim it has to the task is through p->scx.ops_state.
It can be argued that getting rid of double locking is still nice but given
that holding_cpu is needed anyway and can play the same role, I'm not sure
how attractive it is. I suppose we can go either way.
Thanks.
--
tejun
next prev parent reply other threads:[~2022-12-06 21:42 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 [this message]
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 ` [PATCHSET RFC] sched: Implement BPF extensible scheduler class 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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