[9] RFR(M): 7194669: CodeCache::mark_for_deoptimization should avoid verifying dependencies multiple times (original) (raw)

Albert Noll albert.noll at oracle.com
Thu Jan 9 06:28:54 PST 2014

Hi all,

could I get reviews for this patch?

bug: https://bugs.openjdk.java.net/browse/JDK-7194669 webrev: http://cr.openjdk.java.net/~anoll/7194669/webrev.00/

Problem: The dependency verification code in CodeCache::mark_for_deoptimization walks over all live nmethods in the code cache and checks all dependencies for each nmethod. This leads to checking the same dependency multiple times which can take a huge amount of time.

Solution: To avoid checking dependencies more than once, dependencies are abstracted by dependency signatures, which consider (i) the type of a dependency and (ii) the identity hashes of the arguments of a dependency. For each dependency that will be checked, a dependency signature is generated and that dependency signature is compared against a set of already checked dependency signatures. If a dependency has already been checked, the check is skipped. Dependency signatures of a specific type are stored in a binary tree to provide a fast lookup. I.e., each dependency type has its own binary tree. The key to the tree is the identity hash of one argument. More details about the data structure are described as comments in the code.

Results: An evaluation of the performance gain shows a 4.3x speedup of dependency checking. More concretely, I used nashorn + octane on a 64-bit Linux Hotspot version. The dependency checking time of the original version is 3888 seconds. The dependency checking time of the optimized version is 902 seconds.

Passed jprt.

Many thanks in advance, Albert

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