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8040140: System.nanoTime() is slow and non-monotonic on OS X

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Reviewed-by: sspitsyn, shade, dholmes, acorn
This commit is contained in:
Staffan Larsen 2014-04-25 07:40:33 +02:00
parent a162ea836e
commit 0ef4fb7100
5 changed files with 76 additions and 61 deletions
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43
hotspot/src/os/bsd/vm/os_bsd.cpp
View File

@ -127,8 +127,12 @@
// global variables
julong os::Bsd::_physical_memory = 0;
#ifdef __APPLE__
mach_timebase_info_data_t os::Bsd::_timebase_info = {0, 0};
volatile uint64_t os::Bsd::_max_abstime = 0;
#else
int (*os::Bsd::_clock_gettime)(clockid_t, struct timespec *) = NULL;
#endif
pthread_t os::Bsd::_main_thread;
int os::Bsd::_page_size = -1;
@ -986,13 +990,15 @@ jlong os::javaTimeMillis() {
return jlong(time.tv_sec) * 1000 + jlong(time.tv_usec / 1000);
}
#ifndef __APPLE__
#ifndef CLOCK_MONOTONIC
#define CLOCK_MONOTONIC (1)
#endif
#endif
#ifdef __APPLE__
void os::Bsd::clock_init() {
// XXXDARWIN: Investigate replacement monotonic clock
mach_timebase_info(&_timebase_info);
}
#else
void os::Bsd::clock_init() {
@ -1007,10 +1013,39 @@ void os::Bsd::clock_init() {
#endif
#ifdef __APPLE__
jlong os::javaTimeNanos() {
const uint64_t tm = mach_absolute_time();
const uint64_t now = (tm * Bsd::_timebase_info.numer) / Bsd::_timebase_info.denom;
const uint64_t prev = Bsd::_max_abstime;
if (now <= prev) {
return prev; // same or retrograde time;
}
const uint64_t obsv = Atomic::cmpxchg(now, (volatile jlong*)&Bsd::_max_abstime, prev);
assert(obsv >= prev, "invariant"); // Monotonicity
// If the CAS succeeded then we're done and return "now".
// If the CAS failed and the observed value "obsv" is >= now then
// we should return "obsv". If the CAS failed and now > obsv > prv then
// some other thread raced this thread and installed a new value, in which case
// we could either (a) retry the entire operation, (b) retry trying to install now
// or (c) just return obsv. We use (c). No loop is required although in some cases
// we might discard a higher "now" value in deference to a slightly lower but freshly
// installed obsv value. That's entirely benign -- it admits no new orderings compared
// to (a) or (b) -- and greatly reduces coherence traffic.
// We might also condition (c) on the magnitude of the delta between obsv and now.
// Avoiding excessive CAS operations to hot RW locations is critical.
// See https://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate
return (prev == obsv) ? now : obsv;
}
#else // __APPLE__
jlong os::javaTimeNanos() {
if (os::supports_monotonic_clock()) {
struct timespec tp;
int status = Bsd::clock_gettime(CLOCK_MONOTONIC, &tp);
int status = Bsd::_clock_gettime(CLOCK_MONOTONIC, &tp);
assert(status == 0, "gettime error");
jlong result = jlong(tp.tv_sec) * (1000 * 1000 * 1000) + jlong(tp.tv_nsec);
return result;
@ -1023,6 +1058,8 @@ jlong os::javaTimeNanos() {
}
}
#endif // __APPLE__
void os::javaTimeNanos_info(jvmtiTimerInfo *info_ptr) {
if (os::supports_monotonic_clock()) {
info_ptr->max_value = ALL_64_BITS;

10
hotspot/src/os/bsd/vm/os_bsd.hpp
View File

@ -58,7 +58,13 @@ class Bsd {
// For signal flags diagnostics
static int sigflags[MAXSIGNUM];
#ifdef __APPLE__
// mach_absolute_time
static mach_timebase_info_data_t _timebase_info;
static volatile uint64_t _max_abstime;
#else
static int (*_clock_gettime)(clockid_t, struct timespec *);
#endif
static GrowableArray<int>* _cpu_to_node;
@ -134,10 +140,6 @@ class Bsd {
// Real-time clock functions
static void clock_init(void);
static int clock_gettime(clockid_t clock_id, struct timespec *tp) {
return _clock_gettime ? _clock_gettime(clock_id, tp) : -1;
}
// Stack repair handling
// none present

4
hotspot/src/os/bsd/vm/os_bsd.inline.hpp
View File

@ -287,7 +287,11 @@ inline int os::set_sock_opt(int fd, int level, int optname,
}
inline bool os::supports_monotonic_clock() {
#ifdef __APPLE__
return true;
#else
return Bsd::_clock_gettime != NULL;
#endif
}
#endif // OS_BSD_VM_OS_BSD_INLINE_HPP

59
hotspot/src/os/solaris/vm/os_solaris.cpp
View File

@ -347,11 +347,7 @@ julong os::physical_memory() {
static hrtime_t first_hrtime = 0;
static const hrtime_t hrtime_hz = 1000*1000*1000;
const int LOCK_BUSY = 1;
const int LOCK_FREE = 0;
const int LOCK_INVALID = -1;
static volatile hrtime_t max_hrtime = 0;
static volatile int max_hrtime_lock = LOCK_FREE; // Update counter with LSB as lock-in-progress
void os::Solaris::initialize_system_info() {
@ -1364,58 +1360,31 @@ void* os::thread_local_storage_at(int index) {
}
// gethrtime can move backwards if read from one cpu and then a different cpu
// getTimeNanos is guaranteed to not move backward on Solaris
// local spinloop created as faster for a CAS on an int than
// a CAS on a 64bit jlong. Also Atomic::cmpxchg for jlong is not
// supported on sparc v8 or pre supports_cx8 intel boxes.
// oldgetTimeNanos for systems which do not support CAS on 64bit jlong
// i.e. sparc v8 and pre supports_cx8 (i486) intel boxes
inline hrtime_t oldgetTimeNanos() {
int gotlock = LOCK_INVALID;
hrtime_t newtime = gethrtime();
for (;;) {
// grab lock for max_hrtime
int curlock = max_hrtime_lock;
if (curlock & LOCK_BUSY) continue;
if (gotlock = Atomic::cmpxchg(LOCK_BUSY, &max_hrtime_lock, LOCK_FREE) != LOCK_FREE) continue;
if (newtime > max_hrtime) {
max_hrtime = newtime;
} else {
newtime = max_hrtime;
}
// release lock
max_hrtime_lock = LOCK_FREE;
return newtime;
}
}
// gethrtime can move backwards if read from one cpu and then a different cpu
// getTimeNanos is guaranteed to not move backward on Solaris
// gethrtime() should be monotonic according to the documentation,
// but some virtualized platforms are known to break this guarantee.
// getTimeNanos() must be guaranteed not to move backwards, so we
// are forced to add a check here.
inline hrtime_t getTimeNanos() {
if (VM_Version::supports_cx8()) {
const hrtime_t now = gethrtime();
// Use atomic long load since 32-bit x86 uses 2 registers to keep long.
const hrtime_t prev = Atomic::load((volatile jlong*)&max_hrtime);
if (now <= prev) return prev; // same or retrograde time;
const hrtime_t prev = max_hrtime;
if (now <= prev) {
return prev; // same or retrograde time;
}
const hrtime_t obsv = Atomic::cmpxchg(now, (volatile jlong*)&max_hrtime, prev);
assert(obsv >= prev, "invariant"); // Monotonicity
// If the CAS succeeded then we're done and return "now".
// If the CAS failed and the observed value "obs" is >= now then
// we should return "obs". If the CAS failed and now > obs > prv then
// If the CAS failed and the observed value "obsv" is >= now then
// we should return "obsv". If the CAS failed and now > obsv > prv then
// some other thread raced this thread and installed a new value, in which case
// we could either (a) retry the entire operation, (b) retry trying to install now
// or (c) just return obs. We use (c). No loop is required although in some cases
// or (c) just return obsv. We use (c). No loop is required although in some cases
// we might discard a higher "now" value in deference to a slightly lower but freshly
// installed obs value. That's entirely benign -- it admits no new orderings compared
// installed obsv value. That's entirely benign -- it admits no new orderings compared
// to (a) or (b) -- and greatly reduces coherence traffic.
// We might also condition (c) on the magnitude of the delta between obs and now.
// We might also condition (c) on the magnitude of the delta between obsv and now.
// Avoiding excessive CAS operations to hot RW locations is critical.
// See http://blogs.sun.com/dave/entry/cas_and_cache_trivia_invalidate
// See https://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate
return (prev == obsv) ? now : obsv;
} else {
return oldgetTimeNanos();
}
}
// Time since start-up in seconds to a fine granularity.

3
hotspot/src/share/vm/runtime/os.hpp
View File

@ -48,6 +48,9 @@
#ifdef TARGET_OS_FAMILY_bsd
# include "jvm_bsd.h"
# include <setjmp.h>
# ifdef __APPLE__
# include <mach/mach_time.h>
# endif
#endif
class AgentLibrary;