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Date: Wed, 11 Feb 2015 17:12:56 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Pawel Moll <pawel.moll@....com>
Cc: ajh mls <ajhmls@...il.com>,
Richard Cochran <richardcochran@...il.com>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>,
Paul Mackerras <paulus@...ba.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
John Stultz <john.stultz@...aro.org>,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
Christopher Covington <cov@...eaurora.org>,
Namhyung Kim <namhyung@...nel.org>,
David Ahern <dsahern@...il.com>,
Thomas Gleixner <tglx@...utronix.de>,
Tomeu Vizoso <tomeu@...euvizoso.net>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
"adrian.hunter@...el.com" <adrian.hunter@...el.com>
Subject: Re: [PATCH v5] perf: Use monotonic clock as a source for timestamps
How about something like the below? I _think_ it should mostly work for
x86, where the tsc is a 64bit wide cycle counter.
I suppose we should extend the perf userpage time data with
time_last_cycle and time_mask if/when we want to make this work on
something with a short counter.
Of course, at that time we also need to somehow deal with that counter
wrapping, its hardly practical to go iterate all possible userpg
instances from a timer handler.
---
Documentation/kernel-parameters.txt | 9 +++++++
arch/x86/kernel/cpu/perf_event.c | 44 ++++++++++++++++++++++++---------
include/linux/perf_event.h | 6 +++++
kernel/events/core.c | 49 ++++++++++++++++++++++++++++++++++---
kernel/time/timekeeping.c | 30 +++++++++++++++++++++++
5 files changed, 123 insertions(+), 15 deletions(-)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 176d4fe4f076..52255676b6e2 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -91,6 +91,7 @@ the beginning of each description states the restrictions within which a
NUMA NUMA support is enabled.
NFS Appropriate NFS support is enabled.
OSS OSS sound support is enabled.
+ PERF Performance events and counters support is enabled.
PV_OPS A paravirtualized kernel is enabled.
PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
PARISC The PA-RISC architecture is enabled.
@@ -2796,6 +2797,14 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
allocator. This parameter is primarily for debugging
and performance comparison.
+ perf_use_local_clock
+ [PERF]
+ Use local_clock() as a source for perf timestamps
+ generation. This was be the default behaviour and
+ this parameter can be used to maintain backward
+ compatibility or on older hardware with expensive
+ monotonic clock source.
+
pf. [PARIDE]
See Documentation/blockdev/paride.txt.
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index b71a7f86d68a..436a66632f76 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1952,6 +1952,35 @@ static struct pmu pmu = {
.flush_branch_stack = x86_pmu_flush_branch_stack,
};
+static void local_clock_user_time(struct perf_event_mmap_page *userpg, u64 now)
+{
+ data = cyc2ns_read_begin();
+
+ userpg->cap_user_time = 1;
+ userpg->time_mult = data->cyc2ns_mul;
+ userpg->time_shift = data->cyc2ns_shift;
+ userpg->time_offset = data->cyc2ns_offset - now;
+
+ userpg->cap_user_time_zero = 1;
+ userpg->time_zero = data->cyc2ns_offset;
+
+ cyc2ns_read_end(data);
+}
+
+extern void notrace __ktime_get_mono_fast(u64 *offset, u32 *mult, u16 *shift);
+
+static void ktime_fast_mono_user_time(struct perf_event_mmap_page *userpg, u64 now)
+{
+ userpg->cap_user_time = 1;
+ userpg->cap_user_time_zero = 1;
+
+ __ktime_get_mono_fast(&userpg->time_zero,
+ &userpg->time_mult,
+ &userpg->time_shift);
+
+ userpg->offset = userpg->time_zero - now;
+}
+
void arch_perf_update_userpage(struct perf_event *event,
struct perf_event_mmap_page *userpg, u64 now)
{
@@ -1966,17 +1995,10 @@ void arch_perf_update_userpage(struct perf_event *event,
if (!sched_clock_stable())
return;
- data = cyc2ns_read_begin();
-
- userpg->cap_user_time = 1;
- userpg->time_mult = data->cyc2ns_mul;
- userpg->time_shift = data->cyc2ns_shift;
- userpg->time_offset = data->cyc2ns_offset - now;
-
- userpg->cap_user_time_zero = 1;
- userpg->time_zero = data->cyc2ns_offset;
-
- cyc2ns_read_end(data);
+ if (static_key_false(&perf_use_local_clock_key))
+ local_clock_user_time(userpg, now);
+ else
+ ktime_fast_mono_user_time(userpg, now);
}
/*
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 33262004c310..1d61f968113a 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -561,6 +561,12 @@ extern void perf_pmu_enable(struct pmu *pmu);
extern int perf_event_task_disable(void);
extern int perf_event_task_enable(void);
extern int perf_event_refresh(struct perf_event *event, int refresh);
+
+extern struct static_key perf_use_local_clock_key = STATIC_KEY_INIT_FALSE;
+extern void __weak
+arch_perf_update_userpage(struct perf_event *event,
+ struct perf_event_mmap_page *userpg, u64 now);
+
extern void perf_event_update_userpage(struct perf_event *event);
extern int perf_event_release_kernel(struct perf_event *event);
extern struct perf_event *
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 13209a90b751..7bad385103ea 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -42,6 +42,8 @@
#include <linux/module.h>
#include <linux/mman.h>
#include <linux/compat.h>
+#include <linux/sysctl.h>
+#include <linux/jump_label.h>
#include "internal.h"
@@ -322,9 +324,43 @@ extern __weak const char *perf_pmu_name(void)
return "pmu";
}
+struct static_key perf_use_local_clock_key = STATIC_KEY_INIT_FALSE;
+static bool perf_use_local_clock_param __initdata;
+static int __init perf_use_local_clock_setup(char *__unused)
+{
+ perf_use_local_clock_param = true;
+ return 1;
+}
+__setup("perf_use_local_clock", perf_use_local_clock_setup);
+
+static int sysctl_perf_sample_time_clk_id = CLOCK_MONOTONIC;
+
+static struct ctl_table perf_sample_time_kern_table[] = {
+ {
+ .procname = "perf_sample_time_clk_id",
+ .data = &sysctl_perf_sample_time_clk_id,
+ .maxlen = sizeof(int),
+ .mode = 0444,
+ .proc_handler = proc_dointvec,
+ },
+ {}
+};
+
+static struct ctl_table perf_sample_time_root_table[] = {
+ {
+ .procname = "kernel",
+ .mode = 0555,
+ .child = perf_sample_time_kern_table,
+ },
+ {}
+};
+
static inline u64 perf_clock(void)
{
- return local_clock();
+ if (static_key_false(&perf_use_local_clock_key))
+ return local_clock();
+ else
+ return ktime_get_mono_fast_ns();
}
static inline struct perf_cpu_context *
@@ -4101,8 +4137,8 @@ static void perf_event_init_userpage(struct perf_event *event)
rcu_read_unlock();
}
-void __weak arch_perf_update_userpage(
- struct perf_event *event, struct perf_event_mmap_page *userpg, u64 now)
+void __weak arch_perf_update_userpage(struct perf_event *event,
+ struct perf_event_mmap_page *userpg, u64 now)
{
}
@@ -4487,7 +4523,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
if (vma->vm_flags & VM_WRITE)
flags |= RING_BUFFER_WRITABLE;
- rb = rb_alloc(nr_pages,
+ rb = rb_alloc(nr_pages,
event->attr.watermark ? event->attr.wakeup_watermark : 0,
event->cpu, flags);
@@ -8516,6 +8552,11 @@ void __init perf_event_init(void)
*/
BUILD_BUG_ON((offsetof(struct perf_event_mmap_page, data_head))
!= 1024);
+
+ if (perf_use_local_clock_param)
+ static_key_slow_inc(&perf_use_local_clock_key);
+ else
+ register_sysctl_table(perf_sample_time_root_table);
}
static int __init perf_event_sysfs_init(void)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index b124af259800..37bed5931a91 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -334,6 +334,36 @@ u64 notrace ktime_get_mono_fast_ns(void)
}
EXPORT_SYMBOL_GPL(ktime_get_mono_fast_ns);
+void notrace __ktime_get_mono_fast(u64 *offset, u32 *mult, u16 *shift)
+{
+ struct tk_read_base *tkr;
+ unsigned int seq;
+ cycle_t cycle_now, delta;
+ u64 nsecs, now;
+
+ do {
+ seq = raw_read_seqcount(&tk_fast_mono.seq);
+ tkr = tk_fast_mono.base + (seq & 0x01);
+
+ cycle_now = tkr->read(tkr->clock);
+ delta = clocksource_delta(cycle_now, tkr->cycle_last, tkr->mask);
+
+ nsec = delta * tkr->mult + tkr->xtime_nsec;
+ nsec >>= tkr->shift;
+ nsec += arch_gettimeoffset();
+
+ now = ktime_to_ns(tkr->base_mono) + nsec;
+
+ *mult = tkr->mult;
+ *shift = tkr->shift;
+
+ nsec = mul_u64_u32_shr(cycle_now, tkr->mult, tkr->shift);
+
+ *offset = now - nsec;
+
+ } while (read_seqcount_retry(&tk_fast_mono.seq, seq));
+}
+
#ifdef CONFIG_GENERIC_TIME_VSYSCALL_OLD
static inline void update_vsyscall(struct timekeeper *tk)
--
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