linux-kernel - Re: Where is RLIMIT_RT

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Date:	Fri, 14 Jul 2006 22:31:41 +0100 (BST)
From:	Esben Nielsen <nielsen.esben@...glemail.com>
To:	Jean-Marc Valin <Jean-Marc.Valin@...erbrooke.ca>
cc:	Lee Revell <rlrevell@...-job.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: Where is RLIMIT_RT_CPU?



On Fri, 14 Jul 2006, Jean-Marc Valin wrote:

>> It was not merged.
>>
>> This problem should be addressed by a userspace RT watchdog.  Ubuntu
>> should not have shipped their system with unlimited non-root realtime
>> enabled and no watchdog.
>
> Does such a daemon currently exist? Even then, is there any way to
> police all unprivileged RT apps without introducing an O(N) operation
> running continuously at max rt priority? Sort of defeats the purpose of
> having an O(1) scheduler, no? I assume the RT check can be some in O(1)
> time in the kernel, right?
>

Can't you just make a prio 1 task which signals a prio 99 once say every 
second. If the priority 99 task doesn't get the signal after say 2 
seconds, it will look for a rt task running wild. At worst it will have to do
an O(n) algorith when things have gone wrong, not when everything is 
working.

Esben

> About Ubuntu, I agree it wasn't a smart thing to do (I'm not an Ubuntu
> devel, so I don't know what the reason was), but it would be nice if
> this could be fixed without having to entirely remove the unprivileged
> real-time feature. In the end, I'm not sure what the best solution is
> (just an RT audio developer).
>
> 	Jean-Marc
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