linux-kernel - Re: [PATCH] sched: Relax a restriction in sched_rt_can

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 5 May 2015 16:10:49 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Zefan Li <lizefan@...wei.com>
Cc:	Mike Galbraith <umgwanakikbuti@...il.com>,
	Ingo Molnar <mingo@...nel.org>, Tejun Heo <tj@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH] sched: Relax a restriction in sched_rt_can_attach()

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.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/