Re: halt and schedule

From: Richard B. Johnson (root@chaos.analogic.com)
Date: Mon Nov 04 2002 - 12:46:57 EST


On Mon, 4 Nov 2002, wrote:

>
> I have been changing 2.4.19 to run on some new hardware, X86
> based. The system boots and runs off a ramdisk. I am having
> problems which I see as pauses. The system starts up and loads
> the kernel. All seems ok until the ramdisk is mouned and INIT is
> started. From this point on the system appears to stop responding
> for a few seconds and then start again. Eventually, when logged in
> command input can be slow with pauses between entering a
> character and the console displaying the character.
>
>
> I have tried to debug this and found that the kernel is in the
> cpu_idle() routine which is repeatedly calling default_idle() and
> safe_halt(). If you then type a character on the console, using a
> scope, you can see the interrupt being serviced and a character
> being taken from the RX fifo, quickly. However there is no
> response for some seconds. I have also noticed that if you keep the
> thing busy with a benchmark or something simple like ls -lR there is
> no pause.
>
> I noticed that to get out of this loop the kernel is looking for a
> process to schedule. It is as if the process is not being scheduled
> as soon as it could be.
>
> One point to consider is that this board has no RTC or CTC just the
> timer wired to a 10ms interrupt.
>
> I suspect that this is a hardware problem but I don't really know
> where to start looking. Can anyone help ?
>
> Many thanks
>
> Simon.

Temporarily get rid of the hlt instruction. That will allow
the scheduler to spin. On a real CPU, an interrupt (any interrupt)
is supposed to get you out of a halt. Something seems broken
on your box, but you should be able to get it to "work" by
removing the halt.

Cheers,
Dick Johnson
Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).
   Bush : The Fourth Reich of America

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