[RFC patch 01/15] get_cycles() : kconfig HAVE_GET_CYCLES

From: Mathieu Desnoyers
Date: Thu Oct 16 2008 - 19:58:51 EST

Create a new "HAVE_GET_CYCLES" architecture option to specify which
architectures provide 64-bits TSC counters readable with get_cycles(). It's
principally useful to only enable high-precision tracing code only on such
architectures and don't even bother building it on architectures which lack such

It also requires architectures to provide get_cycles_barrier() and

I mainly use it for the "priority-sifting rwlock" latency tracing code, which
traces worse-case latency induced by the locking. It also provides the basic
changes needed for the LTTng timestamping infrastructure.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
CC: David Miller <davem@xxxxxxxxxxxxx>
CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxxxxx>
CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
CC: linux-arch@xxxxxxxxxxxxxxx
init/Kconfig | 10 ++++++++++
1 file changed, 10 insertions(+)

Index: linux-2.6-lttng/init/Kconfig
--- linux-2.6-lttng.orig/init/Kconfig 2008-10-16 11:25:07.000000000 -0400
+++ linux-2.6-lttng/init/Kconfig 2008-10-16 11:32:26.000000000 -0400
@@ -323,6 +323,16 @@ config CPUSETS

+# Architectures with a 64-bits get_cycles() should select this.
+# They should also define
+# get_cycles_barrier() : instruction synchronization barrier if required
+# get_cycles_rate() : cycle counter rate, in HZ. If 0, TSC are not synchronized
+# across CPUs or their frequency may vary due to frequency scaling.
+ def_bool n
bool "Group CPU scheduler"

Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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