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

Vitaly Davidovich vitalyd at gmail.com
Thu Jan 9 06:49:47 PST 2014

Hi Albert,

Just a thought - since you don't care about order of dependencies (just
uniqueness) wouldn't a hashing container be more optimal than binary search


Sent from my phone
On Jan 9, 2014 9:30 AM, "Albert Noll" <albert.noll at oracle.com> wrote:

> 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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