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

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Date:	Thu, 16 Oct 2008 22:08:13 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	David Miller <davem@...emloft.net>
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)

* David Miller (davem@...emloft.net) wrote:
> 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.

I guess you are talking about using sparc64_get_clock_tick rather than
CLOCK_TICK_RATE ? I assume sparc64_get_clock_tick() done on any CPU will
return the same rate ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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