From: Adrian Hunter Date: Fri, 28 Jun 2013 13:22:18 +0000 (+0300) Subject: perf/x86: Add ability to calculate TSC from perf sample timestamps X-Git-Tag: firefly_0821_release~176^2~5456^3~31 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=c73deb6aecda2955716f31572516f09d930ef450;p=firefly-linux-kernel-4.4.55.git 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: Adrian Hunter Signed-off-by: Peter Zijlstra Cc: "H. Peter Anvin" Link: http://lkml.kernel.org/r/1372425741-1676-3-git-send-email-adrian.hunter@intel.com Signed-off-by: Ingo Molnar --- diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h index c91e8b9d588b..235be70d5bb4 100644 --- a/arch/x86/include/asm/tsc.h +++ b/arch/x86/include/asm/tsc.h @@ -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; diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c index a7c7305030cc..8355c84b9729 100644 --- a/arch/x86/kernel/cpu/perf_event.c +++ b/arch/x86/kernel/cpu/perf_event.c @@ -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); + } } /* diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 6ff49247edf8..930e5d48f560 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -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) { diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h index 0041aedf2297..efef1d37a371 100644 --- a/include/uapi/linux/perf_event.h +++ b/include/uapi/linux/perf_event.h @@ -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.