From: Peter Zijlstra <peterz@infradead.org>
To: Zefan Li <lizefan@huawei.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>,
Ingo Molnar <mingo@kernel.org>, Tejun Heo <tj@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Cgroups <cgroups@vger.kernel.org>
Subject: Re: [PATCH] sched: Relax a restriction in sched_rt_can_attach()
Date: Tue, 5 May 2015 16:10:49 +0200 [thread overview]
Message-ID: <20150505141049.GN21418@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <55483EF7.7070905@huawei.com>
On Tue, May 05, 2015 at 11:54:31AM +0800, Zefan Li wrote:
> But I was wondering if we can change the default value of cpu.rt_runtime_us
> from 0 to -1? So by default the RT tasks can be attached to a newly-created
> cgroup without users having to make any configuration, and those tasks are
> confined by the parent cgroup, which is what we have with cfs bw control.
> This require some changes to the code, but I guess it's do-able?
Its tricky.
Imagine:
root
/ \
A B
/ \ / \
a1 a2 b1 b2
Now if they all have -1, I cannot set a bw on any except the leaf nodes
([ab][12]). Because the sum of child bw must strictly be smaller or
equal to the parent bandwidth, and -1 if effective inf.
Similarly, if A has bw enabled I cannot create a new child with -1.
Because above.
Now you can kludge around some of this, for example you can make the
default depend on the parent setting etc.. But that's horribly
inconsistent.
So I really prefer not to go that way; if people use RR/FIFO they had
better bloody know what they're doing; which includes setting up the
system.
The whole RR/FIFO thing is so enormously broken (by definition; this
truly is unfixable) that you simply _cannot_ automate it.
next prev parent reply other threads:[~2015-05-05 14:12 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-04 0:54 [PATCH] sched: Relax a restriction in sched_rt_can_attach() Zefan Li
2015-05-04 3:13 ` Mike Galbraith
2015-05-04 4:39 ` Zefan Li
2015-05-04 5:10 ` Mike Galbraith
2015-05-04 5:39 ` Mike Galbraith
2015-05-04 9:11 ` Zefan Li
2015-05-04 12:08 ` Mike Galbraith
2015-05-04 12:37 ` Peter Zijlstra
2015-05-04 14:09 ` Mike Galbraith
2015-05-05 3:46 ` Zefan Li
2015-05-05 6:02 ` Mike Galbraith
2015-05-05 3:54 ` Zefan Li
2015-05-05 14:10 ` Peter Zijlstra [this message]
2015-05-05 14:18 ` Tejun Heo
2015-05-05 15:19 ` Peter Zijlstra
2015-05-05 16:31 ` Tejun Heo
2015-05-05 19:00 ` Peter Zijlstra
2015-05-05 19:06 ` Tejun Heo
2015-05-06 8:49 ` Peter Zijlstra
2015-05-05 14:41 ` Tejun Heo
2015-05-05 15:11 ` Peter Zijlstra
2015-05-05 16:13 ` Tejun Heo
2015-05-05 16:50 ` Peter Zijlstra
2015-05-05 18:29 ` Thomas Gleixner
2015-05-05 19:00 ` Tejun Heo
2015-05-06 9:12 ` Thomas Gleixner
2015-05-05 18:31 ` Tejun Heo
2015-05-05 14:09 ` Tejun Heo
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