linux-kernel - Re: [RESEND][RFC v3 PATCH] RTTIME watchdog timer proc interface

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Date:	Thu, 3 Apr 2008 16:11:06 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, a.p.zijlstra@...llo.nl
Subject: Re: [RESEND][RFC v3 PATCH] RTTIME watchdog timer proc interface

On Thu, 03 Apr 2008 15:43:25 -0700
Hiroshi Shimamoto <h-shimamoto@...jp.nec.com> wrote:

> From: Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
> 
> Introduce new proc interface for RTTIME watchdog.
> It makes administrator able to set RTTIME watchdog to exisiting real-time
> applications without impact. It's useful we don't want to change software
> stack, but want to use RTTIME watchdog for that software.

Well you don't really need to change the software stack.  It's a matter of
setting RLIMIT_RTTIME in the parent process before starting the stack up. 
This is not much more work than poking at /proc/<pid>/rttime afterwards.

Although setting RLIMIT_RTTIME via fork() is much less useful than being
able to alter it at runtime.

>  fs/proc/base.c |  103 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++

And that's rather a lot of new code just for RLIMIT_RTTIME.  And
RLIMIT_RTTIME is not the only rlimit which has this problem - generally the
rlimit interface is a rather nasty one.

I think we should look at creating a general way of modifying and reading a
running process's rlimits.  If we want to do that, a syscall would be the
appropriate interface.

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