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

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Date:	Fri, 26 Jun 2009 09:36:32 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Paul Mundt <lethal@...ux-sh.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: register_timer_hook use in arch/sh/oprofile

On Fri, 2009-06-26 at 09:23 +0200, Ingo Molnar wrote:
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Wed, 2009-06-24 at 15:24 +0200, Ingo Molnar wrote:
> > > 
> > > [ And long-term analysis ('perf stat' type of runs) dont need IRQs 
> > >   anyway - perfcounters reads outs the counts and summarizes them 
> > >   across the measured workload. ]
> > 
> > If the counter width is less than 64 bits we do need to have some 
> > interrupt to read them from before they cycle so we can accumulate 
> > the deltas into a proper u64.
> 
> Yeah - but even that can be driven from some housekeeping hrtimer.

Oh absolutely, but its one of those things one should not forget to do.

> > But for proper 64 bit hardware counters there is indeed no need 
> > for that.
> 
> Indeed - although they are rare.

Paul Mundt mentioned he had some.
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