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Subject[tip:perf/core] perf/x86: Add ability to calculate TSC from perf sample timestamps
Commit-ID:  c73deb6aecda2955716f31572516f09d930ef450
Gitweb: http://git.kernel.org/tip/c73deb6aecda2955716f31572516f09d930ef450
Author: Adrian Hunter <adrian.hunter@intel.com>
AuthorDate: Fri, 28 Jun 2013 16:22:18 +0300
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 23 Jul 2013 12:17:45 +0200

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 <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>
---
arch/x86/include/asm/tsc.h | 1 +
arch/x86/kernel/cpu/perf_event.c | 6 ++++++
arch/x86/kernel/tsc.c | 6 ++++++
include/uapi/linux/perf_event.h | 22 ++++++++++++++++++++--
4 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index c91e8b9..235be70 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 a7c7305..8355c84 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 6ff4924..930e5d4 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 0041aed..efef1d3 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.

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