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From: "Michal Koutný" <mkoutny@suse.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>,
	joel@joelfernandes.org, chris.hyser@oracle.com,
	joshdon@google.com, mingo@kernel.org, vincent.guittot@linaro.org,
	valentin.schneider@arm.com, mgorman@suse.de,
	linux-kernel@vger.kernel.org, tglx@linutronix.de,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Zefan Li <lizefan.x@bytedance.com>
Subject: Re: [PATCH 0/9] sched: Core scheduling interfaces
Date: Thu, 8 Apr 2021 15:25:52 +0200	[thread overview]
Message-ID: <YG8EYKgcwLCfIZAV@blackbook> (raw)
In-Reply-To: <YG37MBLBIXIPVv7u@hirez.programming.kicks-ass.net>

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On Wed, Apr 07, 2021 at 08:34:24PM +0200, Peter Zijlstra <peterz@infradead.org> wrote:
> IMO as long as cgroups have that tasks file, you get to support people
> using it. That means that tasks joining your cgroup need to 'inherit'
> cgroup properties.
The tasks file is consequence of binding this to cgroups, I'm one step
back. Why to make "core isolation" a cgroup property?

(I understand this could help "visualize" what the common domains are if
cgroups were the only API but with prctl the structure can be
arbitrarily modified anyway.)


> Given something like:
> 
>         R
>        / \
>       A   B
>          / \
>         C   D
Thanks for the example. 

> B group can set core_sched=1 and then all its (and its decendants) tasks
> get to have the same (group) cookie and cannot share with others.
The same could be achieved with the first task of group B allocating its
new cookie which would be inherited in its descednants.

> If however B is a delegate and has a subgroup D that is security
> sensitive and must not share core resources with the rest of B, then it
> can also set D.core_sched=1, such that D (and its decendants) will have
> another (group) cookie.
If there is such a sensitive descendant task, it could allocate a new
cookie (same way as the first one in B did).

> On top of this, say C has a Real-Time tasks, that wants to limit SMT
> interference, then it can set a (task/prctl) cookie on itself, such that
> it will not share the core with the rest of the tasks of B.
(IIUC, in this particular example it'd be redundant if B had no inner
tasks since D isolated itself already.)
Yes, so this is again the same pattern as the tasks above have done.

> In that scenario the D subtree is a restriction (doesn't share) with the
> B subtree.
This implies D's isolation from everything else too, not just B's
members, no?

> And all of B is a restriction on all its tasks, including the Real-Time
> task that set a task cookie, in that none of them can share with tasks
> outside of B (including system tasks which are in R), irrespective of
> what they do with their task cookie.
IIUC, the equivalent restriction could be achieved with the PTRACE-like
check in the prctl API too (with respectively divided uids).

I'm curious whether the cgroup API actually simplifies things that are
possible with the clone/prctl API or allows anything that wouldn't be
otherwise possible.

Regards,
Michal


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  reply	other threads:[~2021-04-08 13:26 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-01 13:10 Peter Zijlstra
2021-04-01 13:10 ` [PATCH 1/9] sched: Allow sched_core_put() from atomic context Peter Zijlstra
2021-04-01 13:10 ` [PATCH 2/9] sched: Implement core-sched assertions Peter Zijlstra
2021-04-01 13:10 ` [PATCH 3/9] sched: Trivial core scheduling cookie management Peter Zijlstra
2021-04-01 20:04   ` Josh Don
2021-04-02  7:13     ` Peter Zijlstra
2021-04-01 13:10 ` [PATCH 4/9] sched: Default core-sched policy Peter Zijlstra
2021-04-21 13:33   ` Peter Zijlstra
2021-04-21 14:31     ` Chris Hyser
2021-04-01 13:10 ` [PATCH 5/9] sched: prctl() core-scheduling interface Peter Zijlstra
2021-04-07 17:00   ` Peter Zijlstra
2021-04-18  3:52     ` Joel Fernandes
2021-04-01 13:10 ` [PATCH 6/9] kselftest: Add test for core sched prctl interface Peter Zijlstra
2021-04-01 13:10 ` [PATCH 7/9] sched: Cgroup core-scheduling interface Peter Zijlstra
2021-04-02  0:34   ` Josh Don
2021-04-01 13:10 ` [PATCH 8/9] rbtree: Remove const from the rb_find_add() comparator Peter Zijlstra
2021-04-01 13:10 ` [PATCH 9/9] sched: prctl() and cgroup interaction Peter Zijlstra
2021-04-03  1:30   ` Josh Don
2021-04-06 15:12     ` Peter Zijlstra
2021-04-04 23:39 ` [PATCH 0/9] sched: Core scheduling interfaces Tejun Heo
2021-04-05 18:46   ` Joel Fernandes
2021-04-06 14:16     ` Tejun Heo
2021-04-18  1:35       ` Joel Fernandes
2021-04-19  9:00         ` Peter Zijlstra
2021-04-21 13:35           ` Peter Zijlstra
2021-04-21 14:45             ` Chris Hyser
2021-04-06 15:32   ` Peter Zijlstra
2021-04-06 16:08     ` Tejun Heo
2021-04-07 18:39       ` Peter Zijlstra
2021-04-07 16:50   ` Michal Koutný
2021-04-07 18:34     ` Peter Zijlstra
2021-04-08 13:25       ` Michal Koutný [this message]
2021-04-08 15:02         ` Peter Zijlstra
2021-04-09  0:16           ` Josh Don
2021-04-19 11:30       ` Tejun Heo
2021-04-20  1:17         ` Josh Don

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