linux-kernel - Re: [RFC patch 04/15] get_cycles() : powerpc64 HAVE_GET

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Date:	Thu, 16 Oct 2008 18:42:52 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	mathieu.desnoyers@...ymtl.ca
Cc:	paulus@...ba.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, mingo@...e.hu,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	rostedt@...dmis.org, a.p.zijlstra@...llo.nl, tglx@...utronix.de,
	benh@...nel.crashing.org, mingo@...hat.com
Subject: Re: [RFC patch 04/15] get_cycles() : powerpc64 HAVE_GET_CYCLES
 (update)

From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Date: Thu, 16 Oct 2008 20:43:28 -0400

> * Paul Mackerras (paulus@...ba.org) wrote:
> > Mathieu Desnoyers writes:
> > 
> > > This patch selects HAVE_GET_CYCLES and makes sure get_cycles_barrier() and
> > > get_cycles_rate() are implemented.
> > 
> > [snip]
> > 
> > > +static inline cycles_t get_cycles_rate(void)
> > > +{
> > > +	return CLOCK_TICK_RATE;
> > > +}
> > 
> > CLOCK_TICK_RATE is certainly wrong.  You want ppc_tb_freq (declared in
> > asm/time.h).  Or tb_ticks_per_sec, since we seem to have two variables
> > for exactly the same thing, for some reason. :)
> > 
> > Paul.
> 
> Ok, this should work better. Thanks !
> 
> Do you know if mtfb implies an instruction synchronization (isync) ? I
> think that if it does not, the new get_cycles_barrier() might have to be
> used at some locations in the kernel code if more precise timestamp
> order is required.

You'll need to make a similar fix on sparc64.
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