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

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Date:	Thu, 03 Apr 2008 16:48:12 -0700
From:	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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

Andrew Morton wrote:
> 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. 

I think it means all processes have the same RTTIME, I cannot change some
of them, correct?

> 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.
> 
I agreed, using /proc is easy but wrong way.
I'll look for other approach for this.


thanks,
Hiroshi Shimamoto
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