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

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Date:	Thu, 16 Oct 2008 20:43:28 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Miller <davem@...emloft.net>, benh@...nel.crashing.org,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [RFC patch 04/15] get_cycles() : powerpc64 HAVE_GET_CYCLES
	(update)

* 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.

Mathieu


get_cycles() : powerpc64 HAVE_GET_CYCLES

This patch selects HAVE_GET_CYCLES and makes sure get_cycles_barrier() and
get_cycles_rate() are implemented.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC: benh@...nel.crashing.org
CC: paulus@...ba.org
CC: David Miller <davem@...emloft.net>
CC: Linus Torvalds <torvalds@...ux-foundation.org>
CC: Andrew Morton <akpm@...ux-foundation.org>
CC: Ingo Molnar <mingo@...hat.com>
CC: Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Steven Rostedt <rostedt@...dmis.org>
CC: linux-arch@...r.kernel.org
---
 arch/powerpc/Kconfig             |    1 +
 arch/powerpc/include/asm/timex.h |   14 ++++++++++++++
 2 files changed, 15 insertions(+)

Index: linux-2.6-lttng/arch/powerpc/Kconfig
===================================================================
--- linux-2.6-lttng.orig/arch/powerpc/Kconfig	2008-10-16 20:31:33.000000000 -0400
+++ linux-2.6-lttng/arch/powerpc/Kconfig	2008-10-16 20:31:36.000000000 -0400
@@ -122,6 +122,7 @@ config PPC
 	select HAVE_DMA_ATTRS if PPC64
 	select USE_GENERIC_SMP_HELPERS if SMP
 	select HAVE_OPROFILE
+	select HAVE_GET_CYCLES if PPC64
 
 config EARLY_PRINTK
 	bool
Index: linux-2.6-lttng/arch/powerpc/include/asm/timex.h
===================================================================
--- linux-2.6-lttng.orig/arch/powerpc/include/asm/timex.h	2008-10-16 20:31:33.000000000 -0400
+++ linux-2.6-lttng/arch/powerpc/include/asm/timex.h	2008-10-16 20:32:02.000000000 -0400
@@ -9,6 +9,7 @@
 
 #include <asm/cputable.h>
 #include <asm/reg.h>
+#include <asm/time.h>
 
 #define CLOCK_TICK_RATE	1024000 /* Underlying HZ */
 
@@ -46,5 +47,18 @@ static inline cycles_t get_cycles(void)
 #endif
 }
 
+static inline cycles_t get_cycles_rate(void)
+{
+	return tb_ticks_per_sec;
+}
+
+/*
+ * To check : assuming mtfb requires isync to synchronize instruction execution.
+ */
+static inline void get_cycles_barrier(void)
+{
+	isync();
+}
+
 #endif	/* __KERNEL__ */
 #endif	/* _ASM_POWERPC_TIMEX_H */

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