Re: [RFC patch 04/15] get_cycles() : powerpc64 HAVE_GET_CYCLES (update)

Mathieu Desnoyers
2008-10-17T00:43:28Z

* 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.

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@polymtl.ca>
CC: benh@kernel.crashing.org
CC: paulus@samba.org
CC: David Miller <davem@davemloft.net>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Ingo Molnar <mingo@redhat.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: linux-arch@vger.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 */