linux-kernel - Re: [RFC][PATCH 0/1] MAZE: Mazed processes monitor

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Date:	Thu, 22 May 2008 18:31:25 +0900
From:	Hirofumi Nakagawa <hnakagawa@...aclelinux.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [RFC][PATCH 0/1] MAZE: Mazed processes monitor

Hi Andi,

Thank you for your comment and proposal.

> How about you implement a way to change the RLIMIT_CPU limit
> of a running task (and possibly fix it to use a finer grained unit
> if you need <1s resolution).
>
> Then you could run a user space daemon running with lower priority that just regularly resets the RLIMIT_CPUs of all running processes.
>
> If some RT process uses so much time that the user daemon cannot
> keep up its cpu time limit will be eventually exceeded and it will
> be killed.
>
> I think that would be a far cleaner and generic way to implement
> this.
>
> -Andi

I also watch normal processes, which run into infinite loop but
cleanly scheduled out by sched when a time slice expires.
In this case, your deamon still can reset the counter.

> Isn't that very similar to RLIMIT_CPU? The main difference seems to be
> that they're regularly reset and that they can be more fine grained
> than seconds.

The differences with MAZE and rlimit are as follows.
  - MAZE detects excessive CPU cycle usage, but rlimits limits total amount
    of CPU usage.
    MAZE can safely handle CPU intensive but correctly running processes.

  - User processes can add watched processes in MAZE.

  - MAZE allows users to choose a way how to act on the process,
    selecting which signal to send.

Following example shows the differences of features MZE and rlimit

----
void foo(void)
{
     for(;;);
}
----
This code receives a signal shortly,
if registered under either rlimit or MAZE.

----
void foo(void)
{
     for(;;) {
         sleep(1);
     }
}
----
This code receives a signal in case of rlimit.
But, it doesn't receive a signal under MAZE.
There are cases when you need to distinguish these two types.

Thanks.
Hirofumi Nakagawa


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