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Date: Mon, 19 Dec 2011 11:51:33 -0800
From: Arun Sharma <asharma@...com>
To: linux-kernel@...r.kernel.org
Cc: Kumar Sundararajan <kumar@...com>, Arun Sharma <asharma@...com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...e.hu>,
Thomas Gleixner <tglx@...utronix.de>,
john stultz <johnstul@...ibm.com>,
Andy Lutomirski <luto@....EDU>,
Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH 2/2] Add a thread cpu time implementation to vDSO
From: Kumar Sundararajan <kumar@...com>
This primarily speeds up clock_gettime(CLOCK_THREAD_CPUTIME_ID, ..)
We use the following method to compute the thread cpu time:
t0 = process start
t1 = most recent context switch time
t2 = time at which the vsyscall is invoked
thread_cpu_time = sum(time slices between t0 to t1) + (t2 - t1)
= current->se.sum_exec_runtime + now - sched_clock()
At context switch time We stash away
adj_sched_time = sum_exec_runtime - sched_clock()
in a per-cpu struct in the VVAR page (which has now been extended
to two pages) and then compute
thread_cpu_time = adj_sched_time + now
All computations are done in nanosecs on systems where TSC is stable.
If TSC is unstable, we fallback to a regular syscall.
Benchmark data:
Baseline:
for (i = 0; i < 100000000; i++) {
clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts);
sum += ts.tv_sec * NSECS_PER_SEC + ts.tv_nsec;
}
vclock_gettime:
vclock_gettime = dlsym(vdso, "__vdso_clock_gettime");
for (i = 0; i < 100000000; i++) {
(*vclock_gettime)(CLOCK_THREAD_CPUTIME_ID, &ts);
sum += ts.tv_sec * NSECS_PER_SEC + ts.tv_nsec;
}
Baseline: 19.34 secs
vclock_gettime: 4.74 secs
This should speed up profilers that need to query thread
cpu time a lot to do fine-grained timestamps.
No statistically significant regression was detected on x86_64
context switch code. Most archs that don't support vsyscalls
will have this code disabled via jump labels.
Signed-off-by: Kumar Sundararajan <kumar@...com>
Signed-off-by: Arun Sharma <asharma@...com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: john stultz <johnstul@...ibm.com>
Cc: Andy Lutomirski <luto@....EDU>
Cc: Eric Dumazet <eric.dumazet@...il.com>
Cc: linux-kernel@...r.kernel.org
---
arch/x86/include/asm/timer.h | 18 +++++++++++++-----
arch/x86/include/asm/vvar.h | 1 +
arch/x86/kernel/tsc.c | 16 ++++++++++++++++
arch/x86/kernel/vsyscall_64.c | 1 +
arch/x86/vdso/vclock_gettime.c | 36 ++++++++++++++++++++++++++++++++++--
arch/x86/vdso/vma.c | 5 +++++
include/linux/jiffies.h | 16 ++++++++++++++++
kernel/sched.c | 8 ++++++++
8 files changed, 94 insertions(+), 7 deletions(-)
diff --git a/arch/x86/include/asm/timer.h b/arch/x86/include/asm/timer.h
index 431793e..99a3670 100644
--- a/arch/x86/include/asm/timer.h
+++ b/arch/x86/include/asm/timer.h
@@ -55,19 +55,27 @@ DECLARE_PER_CPU(unsigned long long, cyc2ns_offset);
#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
-static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
+static inline unsigned long long ___cycles_2_ns(unsigned long long cyc,
+ unsigned long long scale,
+ unsigned long long offset)
{
unsigned long long quot;
unsigned long long rem;
- int cpu = smp_processor_id();
- unsigned long long ns = per_cpu(cyc2ns_offset, cpu);
+ unsigned long long ns = offset;
quot = (cyc >> CYC2NS_SCALE_FACTOR);
rem = cyc & ((1ULL << CYC2NS_SCALE_FACTOR) - 1);
- ns += quot * per_cpu(cyc2ns, cpu) +
- ((rem * per_cpu(cyc2ns, cpu)) >> CYC2NS_SCALE_FACTOR);
+ ns += quot * scale + ((rem * scale) >> CYC2NS_SCALE_FACTOR);
return ns;
}
+static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
+{
+ int cpu = smp_processor_id();
+ unsigned long long offset = per_cpu(cyc2ns_offset, cpu);
+ unsigned long long scale = per_cpu(cyc2ns, cpu);
+ return ___cycles_2_ns(cyc, scale, offset);
+}
+
static inline unsigned long long cycles_2_ns(unsigned long long cyc)
{
unsigned long long ns;
diff --git a/arch/x86/include/asm/vvar.h b/arch/x86/include/asm/vvar.h
index 0fd7a4a..6710e2a 100644
--- a/arch/x86/include/asm/vvar.h
+++ b/arch/x86/include/asm/vvar.h
@@ -47,5 +47,6 @@
DECLARE_VVAR(0, volatile unsigned long, jiffies)
DECLARE_VVAR(16, int, vgetcpu_mode)
DECLARE_VVAR(128, struct vsyscall_gtod_data, vsyscall_gtod_data)
+DECLARE_VVAR(256, struct vcpu_data, vcpu_data)
#undef DECLARE_VVAR
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index db48336..8e9f52c 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -623,6 +623,8 @@ static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
if (cpu_khz) {
*scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz;
*offset = ns_now - (tsc_now * *scale >> CYC2NS_SCALE_FACTOR);
+ vcpu_data.vpercpu[cpu].cyc2ns = *scale;
+ vcpu_data.vpercpu[cpu].cyc2ns_offset = *offset;
}
sched_clock_idle_wakeup_event(0);
@@ -786,6 +788,8 @@ void mark_tsc_unstable(char *reason)
tsc_unstable = 1;
sched_clock_stable = 0;
disable_sched_clock_irqtime();
+ vcpu_data.thread_cputime_disabled = 1;
+ jump_label_dec(&vcpu_data_enabled);
printk(KERN_INFO "Marking TSC unstable due to %s\n", reason);
/* Change only the rating, when not registered */
if (clocksource_tsc.mult)
@@ -943,6 +947,15 @@ static int __init init_tsc_clocksource(void)
*/
device_initcall(init_tsc_clocksource);
+/* Should be optimized away at compile time */
+static noinline int check_vvar_overflow(void)
+{
+ long vcpu_data_offset = (long) vvaraddr_vcpu_data - VVAR_ADDRESS;
+ size_t size = (vcpu_data_offset + sizeof(vcpu_data)
+ + sizeof(struct vpercpu_data) * CONFIG_NR_CPUS);
+ return (size > VVAR_NUM_PAGES * PAGE_SIZE);
+}
+
void __init tsc_init(void)
{
u64 lpj;
@@ -979,6 +992,9 @@ void __init tsc_init(void)
/* now allow native_sched_clock() to use rdtsc */
tsc_disabled = 0;
+ vcpu_data.tsc_khz = tsc_khz;
+ vcpu_data.thread_cputime_disabled = check_vvar_overflow()
+ || !cpu_has(&boot_cpu_data, X86_FEATURE_RDTSCP);
if (!no_sched_irq_time)
enable_sched_clock_irqtime();
diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index 7960d3a..cdfcedf 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -56,6 +56,7 @@ DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data) =
{
.lock = __SEQLOCK_UNLOCKED(__vsyscall_gtod_data.lock),
};
+DEFINE_VVAR(struct vcpu_data, vcpu_data);
static enum { EMULATE, NATIVE, NONE } vsyscall_mode = NATIVE;
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index 6bc0e72..14d466a 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -18,6 +18,7 @@
#include <asm/vsyscall.h>
#include <asm/fixmap.h>
#include <asm/vgtod.h>
+#include <asm/timer.h>
#include <asm/timex.h>
#include <asm/hpet.h>
#include <asm/unistd.h>
@@ -154,8 +155,32 @@ notrace static noinline int do_monotonic_coarse(struct timespec *ts)
return 0;
}
+notrace static noinline unsigned long do_thread_cpu_time(void)
+{
+ unsigned int p;
+ u_int64_t tscval;
+ unsigned long long adj_sched_time, scale, offset;
+ const struct vcpu_data *vp = &VVAR(vcpu_data);
+ int cpu;
+
+ do {
+ native_read_tscp(&p);
+ cpu = p & 0xfff;
+ adj_sched_time = vp->vpercpu[cpu].adj_sched_time;
+ scale = vp->vpercpu[cpu].cyc2ns;
+ offset = vp->vpercpu[cpu].cyc2ns_offset;
+ rdtscpll(tscval, p);
+ cpu = p & 0xfff;
+ } while (unlikely(adj_sched_time != vp->vpercpu[cpu].adj_sched_time));
+
+ return ___cycles_2_ns(tscval, scale, offset) + adj_sched_time;
+}
+
notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
{
+ unsigned long ns;
+ const struct vcpu_data *vp = &VVAR(vcpu_data);
+
switch (clock) {
case CLOCK_REALTIME:
if (likely(gtod->clock.vclock_mode != VCLOCK_NONE))
@@ -169,6 +194,13 @@ notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
return do_realtime_coarse(ts);
case CLOCK_MONOTONIC_COARSE:
return do_monotonic_coarse(ts);
+ case CLOCK_THREAD_CPUTIME_ID:
+ if (vp->thread_cputime_disabled)
+ break;
+ ns = do_thread_cpu_time();
+ ts->tv_sec = 0;
+ timespec_add_ns(ts, ns);
+ return 0;
}
return vdso_fallback_gettime(clock, ts);
diff --git a/arch/x86/vdso/vma.c b/arch/x86/vdso/vma.c
index 153407c..8b7630e 100644
--- a/arch/x86/vdso/vma.c
+++ b/arch/x86/vdso/vma.c
@@ -10,6 +10,7 @@
#include <linux/init.h>
#include <linux/random.h>
#include <linux/elf.h>
+#include <linux/jump_label.h>
#include <asm/vsyscall.h>
#include <asm/vgtod.h>
#include <asm/proto.h>
@@ -24,6 +25,8 @@ extern unsigned short vdso_sync_cpuid;
extern struct page *vdso_pages[];
static unsigned vdso_size;
+struct jump_label_key vcpu_data_enabled;
+
static void __init patch_vdso(void *vdso, size_t len)
{
Elf64_Ehdr *hdr = vdso;
@@ -66,6 +69,8 @@ static int __init init_vdso(void)
for (i = 0; i < npages; i++)
vdso_pages[i] = virt_to_page(vdso_start + i*PAGE_SIZE);
+ if (!vcpu_data.thread_cputime_disabled)
+ jump_label_inc(&vcpu_data_enabled);
return 0;
}
subsys_initcall(init_vdso);
diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index 265e2c3..d44e6aa 100644
--- a/include/linux/jiffies.h
+++ b/include/linux/jiffies.h
@@ -312,4 +312,20 @@ extern unsigned long nsecs_to_jiffies(u64 n);
#define TIMESTAMP_SIZE 30
+struct vpercpu_data {
+ unsigned long long adj_sched_time;
+ unsigned long long cyc2ns_offset;
+ unsigned long cyc2ns;
+} ____cacheline_aligned;
+
+struct vcpu_data {
+ unsigned int tsc_khz;
+ unsigned int thread_cputime_disabled;
+ struct vpercpu_data vpercpu[0];
+};
+extern struct vcpu_data vcpu_data;
+
+struct jump_label_key;
+extern struct jump_label_key vcpu_data_enabled;
+
#endif
diff --git a/kernel/sched.c b/kernel/sched.c
index d6b149c..b738dd6 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3216,6 +3216,14 @@ static void finish_task_switch(struct rq *rq, struct task_struct *prev)
kprobe_flush_task(prev);
put_task_struct(prev);
}
+
+#if CONFIG_NR_CPUS <= 64
+ if (static_branch(&vcpu_data_enabled)) {
+ int cpu = smp_processor_id();
+ vcpu_data.vpercpu[cpu].adj_sched_time =
+ current->se.sum_exec_runtime - sched_clock();
+ }
+#endif
}
#ifdef CONFIG_SMP
--
1.7.4
--
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