Messages in this thread | | | From | "Arun Srinivas" <> | Subject | Re: problem with printk on SMP-- somebody please help | Date | Tue, 09 Nov 2004 07:55:40 +0530 |
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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? 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?
Please help.
Thanks Arun
>From: Mike Waychison <Michael.Waychison@Sun.COM> >To: Arun Srinivas <getarunsri@hotmail.com> >CC: linux-kernel@vger.kernel.org >Subject: Re: problem with printk-- somebody please help >Date: Mon, 08 Nov 2004 14:47:59 -0500 > >-----BEGIN PGP SIGNED MESSAGE----- >Hash: SHA1 > >Arun Srinivas wrote: > > hi > > > > I am new to the kernel world and would be very glad if somebody could > > help me with this problem. > > > > I am unable to do printk or even a macro call like rdtsc()...(for > > reading the time stamp counter) from within the "activate_task" > > function on a kernel with smp support.But these work under the main > > schedule() function. > > > > I was able to do all these i.e., inside "activate_task" on a kernel > > without smp support.Can anybody suggest a solution as to what could be > > the problem?? > > > > somebody please help. > >I seem to recall that doing so would deadlock your machine. >activate_task is called with the given cpu's runqueue locked. printk >eventually calls release_console_sem, which will wake_up_interruptible, >which will eventually call try_to_wake_up which grabs the same lock. > >I don't think I've ever seen printk work while task_rq_lock'ed. > >Someone correct me if I'm wrong, this is the best I was able to figure >out before giving up. > >- -- >Mike Waychison >Sun Microsystems, Inc. >1 (650) 352-5299 voice >1 (416) 202-8336 voice > >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >NOTICE: The opinions expressed in this email are held by me, >and may not represent the views of Sun Microsystems, Inc. >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >-----BEGIN PGP SIGNATURE----- >Version: GnuPG v1.2.5 (GNU/Linux) >Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org > >iD8DBQFBj81vdQs4kOxk3/MRAlJGAKCIYIgXCkaSXpwGLdsj/WK1BhPOlwCeK6s0 >1pc0XbERKlQKpLIBpObhwZA= >=2DSX >-----END PGP SIGNATURE-----
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