linux-kernel - Re: register_timer_hook use in arch/sh/oprofile

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Date:	Wed, 24 Jun 2009 14:47:55 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Paul Mundt <lethal@...ux-sh.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: register_timer_hook use in arch/sh/oprofile


* Paul Mackerras <paulus@...ba.org> wrote:

> Paul Mundt writes:
> 
> > Yes, that all works fine. My comment was more in reference to 
> > the hardware performance counters that don't have IRQs of their 
> > own, which still need to be tied in to the perf_counter API.
> 
> For them you would need to check in hw_perf_counter_init() that 
> counter->attr.sample_period is zero, and fail with an -EINVAL 
> error if it isn't.

That would make 'perf stat' work - but 'perf top' and 'perf record' 
would not.

But those can be made to work as well without hw IRQ support, if the 
period is simply fed into a special hrtimer, with nanosecs units. 
The resulting sampling wont be "constant period" - but none of the 
tools really mind about that.

	Ingo
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