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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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77
hotspot/src/os/solaris/vm/os_solaris.cpp
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@ -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 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
// 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
// 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
// to (a) or (b) -- and greatly reduces coherence traffic.
// We might also condition (c) on the magnitude of the delta between obs and now.
// Avoiding excessive CAS operations to hot RW locations is critical.
// See http://blogs.sun.com/dave/entry/cas_and_cache_trivia_invalidate
return (prev == obsv) ? now : obsv ;
} else {
return oldgetTimeNanos();
const hrtime_t now = gethrtime();
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 "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;
}
// Time since start-up in seconds to a fine granularity.