On Fri, 6 Nov 2020 02:33:37 GMT, David Holmes <dhol...@openjdk.org> wrote:
>> Changes from @fisk and @dcubed-ojdk to: >> >> - simplify ObjectMonitor list management >> - get rid of Type-Stable Memory (TSM) >> >> This change has been tested with Mach5 Tier[1-3],4,5,6,7,8; no new >> regressions. >> Aurora Perf runs have also been done (DaCapo-h2, Quick Startup/Footprint, >> SPECjbb2015-Tuned-G1, SPECjbb2015-Tuned-ParGC, Volano) >> - a few minor regressions (<= -0.24%) >> - Volano is 6.8% better >> >> Eric C. has also done promotion perf runs on these bits and says "the >> results look fine". > > src/hotspot/share/runtime/synchronizer.hpp line 173: > >> 171: >> 172: static MonitorList _in_use_list; >> 173: static jint _in_use_list_ceiling; > > Can you add some commentary on what this ceiling is as I could not understand > its role just by looking at the code. Thanks. How about this: static MonitorList _in_use_list; // The ratio of the current _in_use_list count to the ceiling is used // to determine if we are above MonitorUsedDeflationThreshold and need // to do an async monitor deflation cycle. The ceiling is increased by // AvgMonitorsPerThreadEstimate when a thread is added to the system // and is decreased by AvgMonitorsPerThreadEstimate when a thread is // removed from the system. // Note: If the _in_use_list max exceeds the ceiling, then // monitors_used_above_threshold() will use the in_use_list max instead // of the thread count derived ceiling because we have used more // ObjectMonitors than the estimated average. static jint _in_use_list_ceiling; > src/hotspot/share/runtime/synchronizer.cpp line 221: > >> 219: >> 220: MonitorList ObjectSynchronizer::_in_use_list; >> 221: // Start the ceiling with one thread: > > This relates to me not understanding what this ceiling is (as commented > elsewhere) but why does this say "start with one thread" when the value of > AvgMonitorsPerThreadEstimate defaults to 1024 ?? The estimate is that a single thread will generate at most 1024 inflated ObjectMonitors on average. I changed the comment like this: // Start the ceiling with the estimate for one thread: jint ObjectSynchronizer::_in_use_list_ceiling = AvgMonitorsPerThreadEstimate; Does that help? ------------- PR: https://git.openjdk.java.net/jdk/pull/642
