tree ae1aa7fed4e9a6c6bbec3fc1c2b85cef173e737c
parent 50f90a44f8cd1928054245cab4cd3bd47a1a6347
author Alex Light <allight@google.com> 1511974855 -0800
committer Alex Light <allight@google.com> 1512147308 -0800

Speed up MterpShouldSwitchInterpreters check

We were often performing a pair of TLS reads in order to determine in
the current thread has any pending asynchronous exceptions (exceptions
thrown by the JVMTI StopThread function). This is quite slow and was
impacting some benchmarks. Since it is expected that asynchronous
exceptions are extremely rare we will first check to see if any
asynchronous exceptions have been sent on the current process. Only if
at least one asynchronous exception has been thrown will we do the
expensive TLS lookups to determine if one has been thrown on the
current thread.

Using a global instance value without synchronization or atomics is ok
here since the checkpoint that actually sets the async_exception_thrown
flag provides synchronization by either occurring on the target thread
or passing the checkpoint.

According to go/lem this gives us a 7% increase on the caffeine
string benchmark.

Test: go/lem runs
Test: ./test.py --host -j50
Bug: 68010816
Change-Id: I62684a5b3a7fc7cc600f5efd2a2393d9c4025917