Re: [PATCH v2 4/4] clock: add perf_clock posix clock

[Paul Bolle <pebolle@tiscali.nl>]

[s/pawell.moll/pawel.moll/]

On Wed, 2015-02-18 at 18:21 +0100, Stephane Eranian wrote:
> This patch is a re-packaging of David's Ahern
> posix perf clock available here:
> 
> 	https://github.com/dsahern/linux/blob/perf-full-monty/README.ahern
> 
> The patch itself is based on Pawel Moll's original post:
> 
> 	https://lkml.org/lkml/2013/3/14/523
> 
> The new clock is call PERF_CLOCK. To use it
> 
> 	#include <time.h>
> 	#include <linux/time.h>
> 
> 	struct timespec ts;
> 
> 	clock_gettime(PERF_CLOCK, &ts);
> 
> Signed-off-by: Stephane Eranian <eranian@google.com>
> ---
>  include/uapi/linux/time.h      |  1 +
>  kernel/time/Kconfig            |  6 +++++
>  kernel/time/Makefile           |  1 +
>  kernel/time/perf_posix_clock.c | 54 ++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 62 insertions(+)
>  create mode 100644 kernel/time/perf_posix_clock.c
> 
> diff --git a/include/uapi/linux/time.h b/include/uapi/linux/time.h
> index e75e1b6..9066bf0 100644
> --- a/include/uapi/linux/time.h
> +++ b/include/uapi/linux/time.h
> @@ -56,6 +56,7 @@ struct itimerval {
>  #define CLOCK_BOOTTIME_ALARM		9
>  #define CLOCK_SGI_CYCLE			10	/* Hardware specific */
>  #define CLOCK_TAI			11
> +#define CLOCK_PERF			12
>  
>  #define MAX_CLOCKS			16
>  #define CLOCKS_MASK			(CLOCK_REALTIME | CLOCK_MONOTONIC)
> diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
> index d626dc9..6e4b707 100644
> --- a/kernel/time/Kconfig
> +++ b/kernel/time/Kconfig
> @@ -201,5 +201,11 @@ config HIGH_RES_TIMERS
>  	  hardware is not capable then this option only increases
>  	  the size of the kernel image.
>  
> +config PERF_CLOCK
> +	tristate "Perf_events posix clock timer source"
> +	help
> +	  This option adds a new posix clock timer source which uses the same time
> +	  source as the perf_events subsystem. It makes it possible to correlate
> +          user level samples with perf_events samples.
>  endmenu
>  endif
> diff --git a/kernel/time/Makefile b/kernel/time/Makefile
> index f622cf2..41cd183 100644
> --- a/kernel/time/Makefile
> +++ b/kernel/time/Makefile
> @@ -14,6 +14,7 @@ obj-$(CONFIG_TICK_ONESHOT)			+= tick-sched.o
>  obj-$(CONFIG_TIMER_STATS)			+= timer_stats.o
>  obj-$(CONFIG_DEBUG_FS)				+= timekeeping_debug.o
>  obj-$(CONFIG_TEST_UDELAY)			+= test_udelay.o
> +obj-$(CONFIG_PERF_CLOCK)			+= perf_posix_clock.o
>  
>  $(obj)/time.o: $(obj)/timeconst.h
>  
> diff --git a/kernel/time/perf_posix_clock.c b/kernel/time/perf_posix_clock.c
> new file mode 100644
> index 0000000..03c58b2
> --- /dev/null
> +++ b/kernel/time/perf_posix_clock.c
> @@ -0,0 +1,54 @@
> +/*
> + * Implements CLOCK_PERF.
> + *
> + * perf_clock is not exported, but for as long as I can remember perf_clock
> + * is local_clock which is exported. Make use of that.
> + *
> + * posix clock implementation by Pawel Moll
> + *     https://lkml.org/lkml/2013/3/14/523
> + *
> + * module by David Ahern, December 2013
> + */
> +#include <linux/version.h>
> +#include <linux/module.h>
> +#include <linux/types.h>
> +#include <linux/kernel.h>
> +#include <linux/time.h>
> +#include <linux/posix-timers.h>
> +
> +static int perf_posix_clock_getres(const clockid_t which_clock,
> +	                struct timespec *tp)
> +{
> +	*tp = ns_to_timespec(TICK_NSEC);
> +	return 0;
> +}
> +
> +static int perf_posix_clock_get(clockid_t which_clock, struct timespec *tp)
> +{
> +	*tp = ns_to_timespec(local_clock());
> +	return 0;
> +}
> +
> +
> +static struct k_clock perf_posix_clock = {
> +	.clock_getres = perf_posix_clock_getres,
> +	.clock_get = perf_posix_clock_get,
> +};
> +
> +static int perf_posix_clock_init(void)
> +{
> +	/* register this character driver */
> +	posix_timers_register_clock(CLOCK_PERF, &perf_posix_clock);
> +
> +	printk(KERN_INFO "perf_clock clock registered\n");
> +
> +	/* no API to unregister a clock so this module cannot be unloaded */
> +	__module_get(THIS_MODULE);
> +
> +	return 0;
> +}
> +
> +module_init(perf_posix_clock_init);
> +
> +MODULE_AUTHOR("David Ahern");
> +MODULE_LICENSE("GPL");