[RFC patch 01/18] get_cycles() : kconfig HAVE_GET_CYCLES

[Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>]

[-- Attachment #1: get-cycles-kconfig-have-get-cycles.patch --]
[-- Type: text/plain, Size: 1935 bytes --]

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
support.

It also requires architectures to provide get_cycles_barrier() and
get_cycles_rate().

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@polymtl.ca>
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
---
 init/Kconfig |   10 ++++++++++
 1 file changed, 10 insertions(+)

Index: linux.trees.git/init/Kconfig
===================================================================
--- linux.trees.git.orig/init/Kconfig	2008-11-07 00:06:07.000000000 -0500
+++ linux.trees.git/init/Kconfig	2008-11-07 00:07:23.000000000 -0500
@@ -330,6 +330,16 @@ config CPUSETS
 config HAVE_UNSTABLE_SCHED_CLOCK
 	bool
 
+#
+# 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.
+#
+config HAVE_GET_CYCLES
+	def_bool n
+
 config GROUP_SCHED
 	bool "Group CPU scheduler"
 	depends on EXPERIMENTAL

-- 
Mathieu Desnoyers
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