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

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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: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Peter 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Adrian Hunter 2013-06-28 16:22:18 +03:00 committed by Ingo Molnar
parent 860f085b74
commit c73deb6aec
4 changed files with 33 additions and 2 deletions
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1
arch/x86/include/asm/tsc.h
View File

@ -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;

6
arch/x86/kernel/cpu/perf_event.c
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@ -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);
}
}
/*

6
arch/x86/kernel/tsc.c
View File

@ -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)
{

22
include/uapi/linux/perf_event.h
View File

@ -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.