Date: Tue, 09 Nov 2004 09:54:56 -0500
From: Mike Waychison <Michael.Waychison@Sun.COM>
Subject: Re: problem with printk on SMP-- somebody please help
In-reply-to: <BAY10-F26KktkpgnkTl0003031e@hotmail.com>
To: Arun Srinivas <getarunsri@hotmail.com>
Cc: linux-kernel@vger.kernel.org
Message-id: <4190DA40.9030407@sun.com>
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Arun Srinivas wrote:
> hi
> 
> I really appreciate your suggestions and as a newcomer eager to learn
> more from you people.
> 
> As I said I was able to do printk anywhere in the sched.c (including
> _activate_task ) on a non-smp kernel and on a smp-kernel I can do it
> only on the main schedule() function.
> Also, I would like to add that I am not able to do the macro rdtsc() for
> reading the timestamp counter in the same function.When I compile the
> kernel it dosent show any error, but just the printk's and rdtsc()'s get
> subdued!
> 
> Well,  with reference to your reply, I have some basic questions:
> 1) on a non-smp kernel will the _activate_task not lock the given runqueue?

The locking is done in schedule().  Read include/linux/spinlock.h to see
how spinlocks differ in the SMP vs non-SMP case.  In the latter case
with spinlock debugging enabled, there is no lock bit and recursively
grabbing a lock is possible (though still not allowed!).

> 2) where is the best place I can do the rdtsc() and printk to read the
> value as to when a task is being scheduled for execution, on a SMP kernel?
> 

No idea wrt to rdtsc.

HTH,

- --
Mike Waychison
Sun Microsystems, Inc.
1 (650) 352-5299 voice
1 (416) 202-8336 voice

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