leandrof/linux
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

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

Browse Source 
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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

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 void mark_tsc_unstable(char *reason);
extern int unsynchronized_tsc(void); extern int unsynchronized_tsc(void);
extern int check_tsc_unstable(void); extern int check_tsc_unstable(void);
extern int check_tsc_disabled(void);
extern unsigned long native_calibrate_tsc(void); extern unsigned long native_calibrate_tsc(void);
extern int tsc_clocksource_reliable; extern int tsc_clocksource_reliable;

6
arch/x86/kernel/cpu/perf_event.c
View File

@ -1884,6 +1884,7 @@ static struct pmu pmu = {
void arch_perf_update_userpage(struct perf_event_mmap_page *userpg, u64 now) void arch_perf_update_userpage(struct perf_event_mmap_page *userpg, u64 now)
{ {
userpg->cap_usr_time = 0; userpg->cap_usr_time = 0;
userpg->cap_usr_time_zero = 0;
userpg->cap_usr_rdpmc = x86_pmu.attr_rdpmc; userpg->cap_usr_rdpmc = x86_pmu.attr_rdpmc;
userpg->pmc_width = x86_pmu.cntval_bits; 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_mult = this_cpu_read(cyc2ns);
userpg->time_shift = CYC2NS_SCALE_FACTOR; userpg->time_shift = CYC2NS_SCALE_FACTOR;
userpg->time_offset = this_cpu_read(cyc2ns_offset) - now; 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); EXPORT_SYMBOL_GPL(check_tsc_unstable);
int check_tsc_disabled(void)
{
return tsc_disabled;
}
EXPORT_SYMBOL_GPL(check_tsc_disabled);
#ifdef CONFIG_X86_TSC #ifdef CONFIG_X86_TSC
int __init notsc_setup(char *str) 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 { struct {
__u64 cap_usr_time : 1, __u64 cap_usr_time : 1,
cap_usr_rdpmc : 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; __u16 time_shift;
__u32 time_mult; __u32 time_mult;
__u64 time_offset; __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 * 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. * Control data for the mmap() data buffer.