Date: Wed, 24 Jun 2009 14:54:06 +0200
From: Martin Schwidefsky <schwidefsky@de.ibm.com>
To: Paul Mundt <lethal@linux-sh.org>
Cc: Ingo Molnar <mingo@elte.hu>, linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: register_timer_hook use in arch/sh/oprofile
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On Wed, 24 Jun 2009 21:34:16 +0900
Paul Mundt <lethal@linux-sh.org> wrote:

> On Wed, Jun 24, 2009 at 02:28:28PM +0200, Martin Schwidefsky wrote:
> > On Wed, 24 Jun 2009 20:29:29 +0900
> > Paul Mundt <lethal@linux-sh.org> wrote:
> > > No. oprofile_timer_init() is only entered if the performance counters
> > > fail to register in the SH7750 case, so there is only one timer hook user
> > > at a time:
> > > 
> > > static int __init oprofile_init(void)
> > > {
> > >         int err;
> > > 
> > >         err = oprofile_arch_init(&oprofile_ops);
> > > 
> > >         if (err < 0 || timer) {
> > >                 printk(KERN_INFO "oprofile: using timer interrupt.\n");
> > >                 oprofile_timer_init(&oprofile_ops);
> > >         }
> > > ...
> > 
> > Oh, I see. That is the reason why the s390 version of
> > oprofile_arch_init returns -ENODEV. It does so to trigger the fallback
> > to the timer_hook. That should work for sh as well, no?
> > 
> It would, yes, but it would also disable access to the SH7750 counters at
> the same time, so we don't really want to do that. The sh7750 counters
> are more like timer based profiling with some extra events that can be
> set and read, so reverting to oprofile_timer_init() would reduce
> functionality.
> 
> My current plan is to migrate things over to the perf_counter API and
> annoy Ingo with my interrupt deprived counters ;-)
> 
> Given that hrtimers are already generically supported there, it should
> tie in much cleaner there than in the oprofile case at least.

Ok, that makes sense. So I guess for now I should stop trying to get
rid of the timer_hook and concentrate to convert the fallback code
in timer_int.c to hrtimer. Then after sh is fully converted to the
perf_counter API we can do the cleanup.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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