JFR periodic events are causing extra allocations

The root cause is logging.
See http://hg.openjdk.java.net/jdk8u/jdk8u-dev/jdk/file/2d946ec6c4f8/src/share/classes/jdk/jfr/internal/RequestEngine.java#l70 - for each periodic hook there is a log line generated which includes string concatenation.
Although a message provider is used and, theoretically, the log message should not be constructed unless it is to be outputted, due to the way how the logger integration was backported to 8u the log message will always be constructed (see http://hg.openjdk.java.net/jdk8u/jdk8u-dev/jdk/file/2d946ec6c4f8/src/share/classes/jdk/jfr/internal/Logger.java#l67).

The proposed fix is to integrate the JDK JFR Logger with the LogJFR flag which is used to control logging in hotspot side of JFR.