Re: [PATCH v4 1/3] perf: Use monotonic clock as a source for timestamps

On Wed, 2015-01-21 at 19:48 +0000, Pawel Moll wrote:

On Wed, 2015-01-21 at 15:52 +0000, Pawel Moll wrote:

quoted

On Mon, 2015-01-05 at 13:00 +0000, Peter Zijlstra wrote:

quoted

On Thu, Nov 06, 2014 at 04:51:56PM +0000, Pawel Moll wrote:

quoted

 Documentation/kernel-parameters.txt |  9 +++++++++
 kernel/events/core.c                | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

quoted

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 4c81a86..8ead8d8 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt

quoted

@@ -2763,6 +2764,14 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			allocator.  This parameter is primarily	for debugging
 			and performance comparison.
 
+	perf_use_local_clock
+			[PERF]
+			Use local_clock() as a source for perf timestamps
+			generation. This was be the default behaviour and
+			this parameter can be used to maintain backward
+			compatibility or on older hardware with expensive
+			monotonic clock source.
+
 	pf.		[PARIDE]
 			See Documentation/blockdev/paride.txt.

So I'm always terminally confused on the naming of kernel parameters,
sometimes things are modules (even when they're not actually =m capable)
and get a module::foo naming or so and sometimes they're not.

I guess you mean module.foo?

quoted

So we want to use the module naming thing or not?

Honestly, I don't mind either way. For one thing ftrace doesn't bother
and just uses __setup() as well.

There's one more thing to this - as far as I remember, the module name
is actually derived from the compilation unit name (at some level of
Kbuild). I may be wrong (will have to double check), but a module
parameter defined in kernel/events/core.c may be called something like
"core.parameter" ;-).

Ok, so it's possible to enforce "perf." prefix:

/* You can override this manually, but generally this should match the
   module name. */
#ifdef MODULE
#define MODULE_PARAM_PREFIX /* empty */
#else
#define MODULE_PARAM_PREFIX KBUILD_MODNAME "."
#endif

So, perf_use_local_clock or perf.use_local_clock? :-)

Pawel