On Thu, Nov 06, 2014 at 04:51:56PM +0000, Pawel Moll wrote:
> Documentation/kernel-parameters.txt | 9 +++++++++
> kernel/events/core.c | 37
> +++++++++++++++++++++++++++++++++++++
> 2 files changed, 46 insertions(+)
> 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
> @@ -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.
So we want to use the module naming thing or not?
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 2b02c9f..5d0aa03 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -322,8 +323,41 @@ extern __weak const char *perf_pmu_name(void)
> return "pmu";
> }
>
> +static bool perf_use_local_clock;
> +static int __init perf_use_local_clock_setup(char *__unused)
> +{
> + perf_use_local_clock = true;
> + return 1;
> +}
> +__setup("perf_use_local_clock", perf_use_local_clock_setup);
> static inline u64 perf_clock(void)
> {
> + if (likely(!perf_use_local_clock))
> + return ktime_get_mono_fast_ns();
> +
> return local_clock();
> }
Since this all is boot time, should we not use things like static_key
and avoid the 'pointless' conditional at runtime?
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