Date: Thu, 16 Oct 2008 22:08:13 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
To: David Miller <davem@davemloft.net>
Cc: paulus@samba.org, torvalds@linux-foundation.org, akpm@linux-foundation.org,
       mingo@elte.hu, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
       rostedt@goodmis.org, a.p.zijlstra@chello.nl, tglx@linutronix.de,
       benh@kernel.crashing.org, mingo@redhat.com
Subject: Re: [RFC patch 04/15] get_cycles() : powerpc64 HAVE_GET_CYCLES
	(update)
Message-ID: <20081017020813.GA32468@Krystal>
References: <20081016234656.055839676@polymtl.ca> <18679.56239.74999.534588@cargo.ozlabs.ibm.com> <20081017004328.GA29768@Krystal> <20081016.184252.193691889.davem@davemloft.net>
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* David Miller (davem@davemloft.net) wrote:
> From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
> Date: Thu, 16 Oct 2008 20:43:28 -0400
> 
> > * Paul Mackerras (paulus@samba.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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