From: Joel Fernandes <joel@joelfernandes.org>
To: Phil Auld <pauld@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Nishanth Aravamudan <naravamudan@digitalocean.com>,
Julien Desfossez <jdesfossez@digitalocean.com>,
Tim Chen <tim.c.chen@linux.intel.com>,
mingo@kernel.org, tglx@linutronix.de, pjt@google.com,
torvalds@linux-foundation.org, vpillai <vpillai@digitalocean.com>,
linux-kernel@vger.kernel.org, fweisbec@gmail.com,
keescook@chromium.org, Aaron Lu <aaron.lwe@gmail.com>,
Aubrey Li <aubrey.intel@gmail.com>,
aubrey.li@linux.intel.com,
Valentin Schneider <valentin.schneider@arm.com>,
Mel Gorman <mgorman@techsingularity.net>,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Paolo Bonzini <pbonzini@redhat.com>,
derkling@google.com
Subject: Re: [PATCH RFC] sched: Add a per-thread core scheduling interface
Date: Thu, 28 May 2020 10:51:46 -0400 [thread overview]
Message-ID: <20200528145146.GB87103@google.com> (raw)
In-Reply-To: <20200524140046.GA5598@lorien.usersys.redhat.com>
On Sun, May 24, 2020 at 10:00:46AM -0400, Phil Auld wrote:
> On Fri, May 22, 2020 at 05:35:24PM -0400 Joel Fernandes wrote:
> > On Fri, May 22, 2020 at 02:59:05PM +0200, Peter Zijlstra wrote:
> > [..]
> > > > > It doens't allow tasks for form their own groups (by for example setting
> > > > > the key to that of another task).
> > > >
> > > > So for this, I was thinking of making the prctl pass in an integer. And 0
> > > > would mean untagged. Does that sound good to you?
> > >
> > > A TID, I think. If you pass your own TID, you tag yourself as
> > > not-sharing. If you tag yourself with another tasks's TID, you can do
> > > ptrace tests to see if you're allowed to observe their junk.
> >
> > But that would require a bunch of tasks agreeing on which TID to tag with.
> > For example, if 2 tasks tag with each other's TID, then they would have
> > different tags and not share.
> >
> > What's wrong with passing in an integer instead? In any case, we would do the
> > CAP_SYS_ADMIN check to limit who can do it.
> >
> > Also, one thing CGroup interface allows is an external process to set the
> > cookie, so I am wondering if we should use sched_setattr(2) instead of, or in
> > addition to, the prctl(2). That way, we can drop the CGroup interface
> > completely. How do you feel about that?
> >
>
> I think it should be an arbitrary 64bit value, in both interfaces to avoid
> any potential reuse security issues.
>
> I think the cgroup interface could be extended not to be a boolean but take
> the value. With 0 being untagged as now.
>
> And sched_setattr could be used to set it on a per task basis.
Yeah, something like this will be needed.
> > > > More seriously, the reason I did it this way is the prctl-tagging is a bit
> > > > incompatible with CGroup tagging:
> > > >
> > > > 1. What happens if 2 tasks are in a tagged CGroup and one of them changes
> > > > their cookie through prctl? Do they still remain in the tagged CGroup but are
> > > > now going to not trust each other? Do they get removed from the CGroup? This
> > > > is why I made the prctl fail with -EBUSY in such cases.
In util-clamp's design (which has task-specific attribute and task-group
attribute), it seems for that the priority is task-specific value first, then
the group one, then the system-wide one.
Perhaps a similar design can be adopted for this interface. So probably we
should let the per-task interface not fail if the task was already in CGroup
and rather prioritize its value first before looking at the group one?
Uclamp's comments:
* The effective clamp bucket index of a task depends on, by increasing
* priority:
* - the task specific clamp value, when explicitly requested from userspace
* - the task group effective clamp value, for tasks not either in the root
* group or in an autogroup
* - the system default clamp value, defined by the sysadmin
> > > >
> > > > 2. What happens if 2 tagged tasks with different cookies are added to a
> > > > tagged CGroup? Do we fail the addition of the tasks to the group, or do we
> > > > override their cookie (like I'm doing)?
> > >
> > > For #2 I think I prefer failure.
> > >
> > > But having the rationale spelled out in documentation (man-pages for
> > > example) is important.
> >
> > If we drop the CGroup interface, this would avoid both #1 and #2.
> >
>
> I believe both are useful. Personally, I think the per-task setting should
> win over the cgroup tagging. In that case #1 just falls out.
Cool, this is similar to what I mentioned above.
> And #2 pretty
> much as well. Nothing would happen to the tagged task as they were added
> to the cgroup. They'd keep their explicitly assigned tags and everything
> should "just work". There are other reasons to be in a cpu cgroup together
> than just the core scheduling tag.
Well ok, so there's no reason to fail them the addition to CGroup of a
prctl-tagged task then, we can let it succeed but prioritize the
task-specific attribute over the group-specific one.
> There are a few other edge cases, like if you are in a cgroup, but have
> been tagged explicitly with sched_setattr and then get untagged (presumably
> by setting 0) do you get the cgroup tag or just stay untagged? I think based
> on per-task winning you'd stay untagged. I supposed you could move out and
> back in the cgroup to get the tag reapplied (Or maybe the cgroup interface
> could just be reused with the same value to re-tag everyone who's untagged).
If we maintain a task-specific tag and a group-specific tag, then I think
both tags can coexist and the final tag is decided on priority basis
mentioned above.
So before getting into CGroup, I think first we develop the task-specific
tagging mechanism like Peter was suggesting. So let us talk about that. I
will reply to the other thread Vineeth started while CC'ing you. In
particular, I like Peter's idea about user land passing a TID to share a core
with.
thanks,
- Joel
>
>
>
> Cheers,
> Phil
>
>
> > thanks,
> >
> > - Joel
> >
>
> --
>
next prev parent reply other threads:[~2020-05-28 14:51 UTC|newest]
Thread overview: 110+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-04 16:59 [RFC PATCH 00/13] Core scheduling v5 vpillai
2020-03-04 16:59 ` [RFC PATCH 01/13] sched: Wrap rq::lock access vpillai
2020-03-04 16:59 ` [RFC PATCH 02/13] sched: Introduce sched_class::pick_task() vpillai
2020-03-04 16:59 ` [RFC PATCH 03/13] sched: Core-wide rq->lock vpillai
2020-04-01 11:42 ` [PATCH] sched/arm64: store cpu topology before notify_cpu_starting Cheng Jian
2020-04-01 13:23 ` Valentin Schneider
2020-04-06 8:00 ` chengjian (D)
2020-04-09 9:59 ` Sudeep Holla
2020-04-09 10:32 ` Valentin Schneider
2020-04-09 11:08 ` Sudeep Holla
2020-04-09 17:54 ` Joel Fernandes
2020-04-10 13:49 ` chengjian (D)
2020-04-14 11:36 ` [RFC PATCH 03/13] sched: Core-wide rq->lock Peter Zijlstra
2020-04-14 21:35 ` Vineeth Remanan Pillai
2020-04-15 10:55 ` Peter Zijlstra
2020-04-14 14:32 ` Peter Zijlstra
2020-03-04 16:59 ` [RFC PATCH 04/13] sched/fair: Add a few assertions vpillai
2020-03-04 16:59 ` [RFC PATCH 05/13] sched: Basic tracking of matching tasks vpillai
2020-03-04 16:59 ` [RFC PATCH 06/13] sched: Update core scheduler queue when taking cpu online/offline vpillai
2020-03-04 16:59 ` [RFC PATCH 07/13] sched: Add core wide task selection and scheduling vpillai
2020-04-14 13:35 ` Peter Zijlstra
2020-04-16 23:32 ` Tim Chen
2020-04-17 10:57 ` Peter Zijlstra
2020-04-16 3:39 ` Chen Yu
2020-04-16 19:59 ` Vineeth Remanan Pillai
2020-04-17 11:18 ` Peter Zijlstra
2020-04-19 15:31 ` Chen Yu
2020-05-21 23:14 ` Joel Fernandes
2020-05-21 23:16 ` Joel Fernandes
2020-05-22 2:35 ` Joel Fernandes
2020-05-22 3:44 ` Aaron Lu
2020-05-22 20:13 ` Joel Fernandes
2020-03-04 16:59 ` [RFC PATCH 08/13] sched/fair: wrapper for cfs_rq->min_vruntime vpillai
2020-03-04 16:59 ` [RFC PATCH 09/13] sched/fair: core wide vruntime comparison vpillai
2020-04-14 13:56 ` Peter Zijlstra
2020-04-15 3:34 ` Aaron Lu
2020-04-15 4:07 ` Aaron Lu
2020-04-15 21:24 ` Vineeth Remanan Pillai
2020-04-17 9:40 ` Aaron Lu
2020-04-20 8:07 ` [PATCH updated] sched/fair: core wide cfs task priority comparison Aaron Lu
2020-04-20 22:26 ` Vineeth Remanan Pillai
2020-04-21 2:51 ` Aaron Lu
2020-04-24 14:24 ` [PATCH updated v2] " Aaron Lu
2020-05-06 14:35 ` Peter Zijlstra
2020-05-08 8:44 ` Aaron Lu
2020-05-08 9:09 ` Peter Zijlstra
2020-05-08 12:34 ` Aaron Lu
2020-05-14 13:02 ` Peter Zijlstra
2020-05-14 22:51 ` Vineeth Remanan Pillai
2020-05-15 10:38 ` Peter Zijlstra
2020-05-15 10:43 ` Peter Zijlstra
2020-05-15 14:24 ` Vineeth Remanan Pillai
2020-05-16 3:42 ` Aaron Lu
2020-05-22 9:40 ` Aaron Lu
2020-06-08 1:41 ` Ning, Hongyu
2020-03-04 17:00 ` [RFC PATCH 10/13] sched: Trivial forced-newidle balancer vpillai
2020-03-04 17:00 ` [RFC PATCH 11/13] sched: migration changes for core scheduling vpillai
2020-06-12 13:21 ` Joel Fernandes
2020-06-12 21:32 ` Vineeth Remanan Pillai
2020-06-13 2:25 ` Joel Fernandes
2020-06-13 18:59 ` Vineeth Remanan Pillai
2020-06-15 2:05 ` Li, Aubrey
2020-03-04 17:00 ` [RFC PATCH 12/13] sched: cgroup tagging interface " vpillai
2020-06-26 15:06 ` Vineeth Remanan Pillai
2020-03-04 17:00 ` [RFC PATCH 13/13] sched: Debug bits vpillai
2020-03-04 17:36 ` [RFC PATCH 00/13] Core scheduling v5 Tim Chen
2020-03-04 17:42 ` Vineeth Remanan Pillai
2020-04-14 14:21 ` Peter Zijlstra
2020-04-15 16:32 ` Joel Fernandes
2020-04-17 11:12 ` Peter Zijlstra
2020-04-17 12:35 ` Alexander Graf
2020-04-17 13:08 ` Peter Zijlstra
2020-04-18 2:25 ` Joel Fernandes
2020-05-09 14:35 ` Dario Faggioli
[not found] ` <38805656-2e2f-222a-c083-692f4b113313@linux.intel.com>
2020-05-09 3:39 ` Ning, Hongyu
2020-05-14 20:51 ` FW: " Gruza, Agata
2020-05-10 23:46 ` [PATCH RFC] Add support for core-wide protection of IRQ and softirq Joel Fernandes (Google)
2020-05-11 13:49 ` Peter Zijlstra
2020-05-11 14:54 ` Joel Fernandes
2020-05-20 22:26 ` [PATCH RFC] sched: Add a per-thread core scheduling interface Joel Fernandes (Google)
2020-05-21 4:09 ` [PATCH RFC] sched: Add a per-thread core scheduling interface(Internet mail) benbjiang(蒋彪)
2020-05-21 13:49 ` Joel Fernandes
2020-05-21 8:51 ` [PATCH RFC] sched: Add a per-thread core scheduling interface Peter Zijlstra
2020-05-21 13:47 ` Joel Fernandes
2020-05-21 20:20 ` Vineeth Remanan Pillai
2020-05-22 12:59 ` Peter Zijlstra
2020-05-22 21:35 ` Joel Fernandes
2020-05-24 14:00 ` Phil Auld
2020-05-28 14:51 ` Joel Fernandes [this message]
2020-05-28 17:01 ` Peter Zijlstra
2020-05-28 18:17 ` Phil Auld
2020-05-28 18:34 ` Phil Auld
2020-05-28 18:23 ` Joel Fernandes
2020-05-21 18:31 ` Linus Torvalds
2020-05-21 20:40 ` Joel Fernandes
2020-05-21 21:58 ` Jesse Barnes
2020-05-22 16:33 ` Linus Torvalds
2020-05-20 22:37 ` [PATCH RFC v2] Add support for core-wide protection of IRQ and softirq Joel Fernandes (Google)
2020-05-20 22:48 ` [PATCH RFC] sched: Use sched-RCU in core-scheduling balancing logic Joel Fernandes (Google)
2020-05-21 22:52 ` Paul E. McKenney
2020-05-22 1:26 ` Joel Fernandes
2020-06-25 20:12 ` [RFC PATCH 00/13] Core scheduling v5 Vineeth Remanan Pillai
2020-06-26 1:47 ` Joel Fernandes
2020-06-26 14:36 ` Vineeth Remanan Pillai
2020-06-26 15:10 ` Joel Fernandes
2020-06-26 15:12 ` Joel Fernandes
2020-06-27 16:21 ` Joel Fernandes
2020-06-30 14:11 ` Phil Auld
2020-06-29 12:33 ` Li, Aubrey
2020-06-29 19:41 ` Vineeth Remanan Pillai
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