src/os/solaris/vm/os_solaris.cpp

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rev 6280 : 8040140: System.nanoTime() is slow and non-monotonic on OS X
Reviewed-by: sspitsyn, shade

*** 1393,1419 **** // gethrtime can move backwards if read from one cpu and then a different cpu // getTimeNanos is guaranteed to not move backward on Solaris 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(); } } --- 1393,1424 ---- // gethrtime can move backwards if read from one cpu and then a different cpu // getTimeNanos is guaranteed to not move backward on Solaris inline hrtime_t getTimeNanos() { if (VM_Version::supports_cx8()) { const hrtime_t now = gethrtime(); ! if (AssumeMonotonicOSTimers) { ! return now; ! } ! ! 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 ; } else { return oldgetTimeNanos(); } }