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From: Greg Kerr <greg@kerrnel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Greg Kerr <kerrnel@google.com>,
	mingo@kernel.org, tglx@linutronix.de,
	Paul Turner <pjt@google.com>,
	tim.c.chen@linux.intel.com, torvalds@linux-foundation.org,
	linux-kernel@vger.kernel.org, subhra.mazumdar@oracle.com,
	fweisbec@gmail.com, keescook@chromium.org
Subject: Re: [RFC][PATCH 00/16] sched: Core scheduling
Date: Wed, 20 Feb 2019 10:33:55 -0800	[thread overview]
Message-ID: <20190220183355.GA213003@kerrnel.com> (raw)
In-Reply-To: <20190220094255.GE32494@hirez.programming.kicks-ass.net>

On Wed, Feb 20, 2019 at 10:42:55AM +0100, Peter Zijlstra wrote:
> 
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?
> A: Top-posting.
> Q: What is the most annoying thing in e-mail?
> 
I am relieved to know that when my mail client embeds HTML tags into raw
text, it will only be the second most annoying thing I've done on
e-mail.

Speaking of annoying things to do, sorry for switching e-mail addresses
but this is easier to do from my personal e-mail.

> On Tue, Feb 19, 2019 at 02:07:01PM -0800, Greg Kerr wrote:
> > Thanks for posting this patchset Peter. Based on the patch titled, "sched: A
> > quick and dirty cgroup tagging interface," I believe cgroups are used to
> > define co-scheduling groups in this implementation.
> > 
> > Chrome OS engineers (kerrnel@google.com, mpdenton@google.com, and
> > palmer@google.com) are considering an interface that is usable by unprivileged
> > userspace apps. cgroups are a global resource that require privileged access.
> > Have you considered an interface that is akin to namespaces? Consider the
> > following strawperson API proposal (I understand prctl() is generally
> > used for process
> > specific actions, so we aren't married to using prctl()):
> 
> I don't think we're anywhere near the point where I care about
> interfaces with this stuff.
> 
> Interfaces are a trivial but tedious matter once the rest works to
> satisfaction.
> 
I agree that the API itself is a bit of a bike shedding and that's why I
provided a strawperson proposal to highlight the desired properties. I
do think the high level semantics are important to agree upon.

Using cgroups could imply that a privileged user is meant to create and
track all the core scheduling groups. It sounds like you picked cgroups
out of ease of prototyping and not the specific behavior?

> As it happens; there is actually a bug in that very cgroup patch that
> can cause undesired scheduling. Try spotting and fixing that.
> 
This is where I think the high level properties of core scheduling are
relevant. I'm not sure what bug is in the existing patch, but it's hard
for me to tell if the existing code behaves correctly without answering
questions, such as, "Should processes from two separate parents be
allowed to co-execute?"

> Another question is if we want to be L1TF complete (and how strict) or
> not, and if so, build the missing pieces (for instance we currently
> don't kick siblings on IRQ/trap/exception entry -- and yes that's nasty
> and horrible code and missing for that reason).
>
I assumed from the beginning that this should be safe across exceptions.
Is there a mitigating reason that it shouldn't?

> 
> So first; does this provide what we need? If that's sorted we can
> bike-shed on uapi/abi.
I agree on not bike shedding about the API, but can we agree on some of
the high level properties? For example, who generates the core
scheduling ids, what properties about them are enforced, etc.?

Regards,

Greg Kerr

  reply	other threads:[~2019-02-20 19:11 UTC|newest]

Thread overview: 99+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-18 16:56 [RFC][PATCH 00/16] sched: Core scheduling Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 01/16] stop_machine: Fix stop_cpus_in_progress ordering Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 02/16] sched: Fix kerneldoc comment for ia64_set_curr_task Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 03/16] sched: Wrap rq::lock access Peter Zijlstra
2019-02-19 16:13   ` Phil Auld
2019-02-19 16:22     ` Peter Zijlstra
2019-02-19 16:37       ` Phil Auld
2019-03-18 15:41   ` Julien Desfossez
2019-03-20  2:29     ` Subhra Mazumdar
2019-03-21 21:20       ` Julien Desfossez
2019-03-22 13:34         ` Peter Zijlstra
2019-03-22 20:59           ` Julien Desfossez
2019-03-23  0:06         ` Subhra Mazumdar
2019-03-27  1:02           ` Subhra Mazumdar
2019-03-29 13:35           ` Julien Desfossez
2019-03-29 22:23             ` Subhra Mazumdar
2019-04-01 21:35               ` Subhra Mazumdar
2019-04-03 20:16                 ` Julien Desfossez
2019-04-05  1:30                   ` Subhra Mazumdar
2019-04-02  7:42               ` Peter Zijlstra
2019-03-22 23:28       ` Tim Chen
2019-03-22 23:44         ` Tim Chen
2019-02-18 16:56 ` [RFC][PATCH 04/16] sched/{rt,deadline}: Fix set_next_task vs pick_next_task Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 05/16] sched: Add task_struct pointer to sched_class::set_curr_task Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 06/16] sched/fair: Export newidle_balance() Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 07/16] sched: Allow put_prev_task() to drop rq->lock Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 08/16] sched: Rework pick_next_task() slow-path Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 09/16] sched: Introduce sched_class::pick_task() Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 10/16] sched: Core-wide rq->lock Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 11/16] sched: Basic tracking of matching tasks Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 12/16] sched: A quick and dirty cgroup tagging interface Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 13/16] sched: Add core wide task selection and scheduling Peter Zijlstra
     [not found]   ` <20190402064612.GA46500@aaronlu>
2019-04-02  8:28     ` Peter Zijlstra
2019-04-02 13:20       ` Aaron Lu
2019-04-05 14:55       ` Aaron Lu
2019-04-09 18:09         ` Tim Chen
2019-04-10  4:36           ` Aaron Lu
2019-04-10 14:18             ` Aubrey Li
2019-04-11  2:11               ` Aaron Lu
2019-04-10 14:44             ` Peter Zijlstra
2019-04-11  3:05               ` Aaron Lu
2019-04-11  9:19                 ` Peter Zijlstra
2019-04-10  8:06           ` Peter Zijlstra
2019-04-10 19:58             ` Vineeth Remanan Pillai
2019-04-15 16:59             ` Julien Desfossez
2019-04-16 13:43       ` Aaron Lu
2019-04-09 18:38   ` Julien Desfossez
2019-04-10 15:01     ` Peter Zijlstra
2019-04-11  0:11     ` Subhra Mazumdar
2019-04-19  8:40       ` Ingo Molnar
2019-04-19 23:16         ` Subhra Mazumdar
2019-02-18 16:56 ` [RFC][PATCH 14/16] sched/fair: Add a few assertions Peter Zijlstra
2019-02-18 16:56 ` [RFC][PATCH 15/16] sched: Trivial forced-newidle balancer Peter Zijlstra
2019-02-21 16:19   ` Valentin Schneider
2019-02-21 16:41     ` Peter Zijlstra
2019-02-21 16:47       ` Peter Zijlstra
2019-02-21 18:28         ` Valentin Schneider
2019-04-04  8:31       ` Aubrey Li
2019-04-06  1:36         ` Aubrey Li
2019-02-18 16:56 ` [RFC][PATCH 16/16] sched: Debug bits Peter Zijlstra
2019-02-18 17:49 ` [RFC][PATCH 00/16] sched: Core scheduling Linus Torvalds
2019-02-18 20:40   ` Peter Zijlstra
2019-02-19  0:29     ` Linus Torvalds
2019-02-19 15:15       ` Ingo Molnar
2019-02-22 12:17     ` Paolo Bonzini
2019-02-22 14:20       ` Peter Zijlstra
2019-02-22 19:26         ` Tim Chen
2019-02-26  8:26           ` Aubrey Li
2019-02-27  7:54             ` Aubrey Li
2019-02-21  2:53   ` Subhra Mazumdar
2019-02-21 14:03     ` Peter Zijlstra
2019-02-21 18:44       ` Subhra Mazumdar
2019-02-22  0:34       ` Subhra Mazumdar
2019-02-22 12:45   ` Mel Gorman
2019-02-22 16:10     ` Mel Gorman
2019-03-08 19:44     ` Subhra Mazumdar
2019-03-11  4:23       ` Aubrey Li
2019-03-11 18:34         ` Subhra Mazumdar
2019-03-11 23:33           ` Subhra Mazumdar
2019-03-12  0:20             ` Greg Kerr
2019-03-12  0:47               ` Subhra Mazumdar
2019-03-12  7:33               ` Aaron Lu
2019-03-12  7:45             ` Aubrey Li
2019-03-13  5:55               ` Aubrey Li
2019-03-14  0:35                 ` Tim Chen
2019-03-14  5:30                   ` Aubrey Li
2019-03-14  6:07                     ` Li, Aubrey
2019-03-18  6:56             ` Aubrey Li
2019-03-12 19:07           ` Pawan Gupta
2019-03-26  7:32       ` Aaron Lu
2019-03-26  7:56         ` Aaron Lu
2019-02-19 22:07 ` Greg Kerr
2019-02-20  9:42   ` Peter Zijlstra
2019-02-20 18:33     ` Greg Kerr [this message]
2019-02-22 14:10       ` Peter Zijlstra
2019-03-07 22:06         ` Paolo Bonzini
2019-02-20 18:43     ` Subhra Mazumdar
2019-03-01  2:54 ` Subhra Mazumdar
2019-03-14 15:28 ` Julien Desfossez

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