lkml.org 
[lkml]   [2013]   [Jun]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 2/5] x86: add ability to calculate TSC from perf sample timestamps
Date
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>
---
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 afc2413..3f74034 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1860,6 +1860,7 @@ 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;

@@ -1873,6 +1874,11 @@ 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 098b3cf..c810283 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 19f6ee5..663be3f 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.
--
1.7.11.7


\
 
 \ /
  Last update: 2013-06-28 16:01    [W:0.173 / U:5.700 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site