Commit c73deb6a authored by Adrian Hunter's avatar Adrian Hunter Committed by Ingo Molnar
Browse files

perf/x86: Add ability to calculate TSC from perf sample timestamps 



For modern CPUs, perf clock is directly related to TSC.  TSC
can be calculated from perf clock and vice versa using a simple
calculation.  Two of the three componenets of that calculation
are already exported in struct perf_event_mmap_page.  This patch
exports the third.

Signed-off-by: default avatarAdrian Hunter <adrian.hunter@intel.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: http://lkml.kernel.org/r/1372425741-1676-3-git-send-email-adrian.hunter@intel.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 860f085b

arch/x86/include/asm/tsc.h

+1 −0
Original line number Diff line number Diff line
@@ -49,6 +49,7 @@ extern void tsc_init(void); 
extern void mark_tsc_unstable(char *reason);

extern int unsynchronized_tsc(void);

extern int check_tsc_unstable(void);

extern int check_tsc_disabled(void);

extern unsigned long native_calibrate_tsc(void);



extern int tsc_clocksource_reliable;

arch/x86/kernel/cpu/perf_event.c

+6 −0
Original line number Diff line number Diff line
@@ -1884,6 +1884,7 @@ static struct pmu pmu = { 
void arch_perf_update_userpage(struct perf_event_mmap_page *userpg, u64 now)

{

	userpg->cap_usr_time = 0;

	userpg->cap_usr_time_zero = 0;

	userpg->cap_usr_rdpmc = x86_pmu.attr_rdpmc;

	userpg->pmc_width = x86_pmu.cntval_bits;
@@ -1897,6 +1898,11 @@ void arch_perf_update_userpage(struct perf_event_mmap_page *userpg, u64 now) 
	userpg->time_mult = this_cpu_read(cyc2ns);

	userpg->time_shift = CYC2NS_SCALE_FACTOR;

	userpg->time_offset = this_cpu_read(cyc2ns_offset) - now;



	if (sched_clock_stable && !check_tsc_disabled()) {

		userpg->cap_usr_time_zero = 1;

		userpg->time_zero = this_cpu_read(cyc2ns_offset);

	}

}



/*

arch/x86/kernel/tsc.c

+6 −0
Original line number Diff line number Diff line
@@ -89,6 +89,12 @@ int check_tsc_unstable(void) 
}

EXPORT_SYMBOL_GPL(check_tsc_unstable);



int check_tsc_disabled(void)

{

	return tsc_disabled;

}

EXPORT_SYMBOL_GPL(check_tsc_disabled);



#ifdef CONFIG_X86_TSC

int __init notsc_setup(char *str)

{

include/uapi/linux/perf_event.h

+20 −2
Original line number Diff line number Diff line
@@ -378,7 +378,8 @@ struct perf_event_mmap_page { 
		struct {

			__u64	cap_usr_time		: 1,

				cap_usr_rdpmc		: 1,

				cap_____res		: 62;

				cap_usr_time_zero	: 1,

				cap_____res		: 61;

		};

	};
@@ -420,12 +421,29 @@ struct perf_event_mmap_page { 
	__u16	time_shift;

	__u32	time_mult;

	__u64	time_offset;

	/*

	 * If cap_usr_time_zero, the hardware clock (e.g. TSC) can be calculated

	 * from sample timestamps.

	 *

	 *   time = timestamp - time_zero;

	 *   quot = time / time_mult;

	 *   rem  = time % time_mult;

	 *   cyc = (quot << time_shift) + (rem << time_shift) / time_mult;

	 *

	 * And vice versa:

	 *

	 *   quot = cyc >> time_shift;

	 *   rem  = cyc & ((1 << time_shift) - 1);

	 *   timestamp = time_zero + quot * time_mult +

	 *               ((rem * time_mult) >> time_shift);

	 */

	__u64	time_zero;



		/*

		 * Hole for extension of the self monitor capabilities

		 */



	__u64	__reserved[120];	/* align to 1k */

	__u64	__reserved[119];	/* align to 1k */



	/*

	 * Control data for the mmap() data buffer.

CRA Git | Maintained and supported by SUSTech CRA and CCSE