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  1. JDK
  2. JDK-8267396

Avoid recording "pc" in unhandled oops detector for better performance

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      b24

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        The motivation is timeouts like JDK-8267348. Note that we are spending a significant amount of time getting pc = os::current_frame() during oop registration.

        As far as I understand from the Hotspot code, that is only to print the PC when the unhandled oops detector fails _itself_:

            // If an entry is on the unhandled oop list but isn't on the stack
            // anymore, it must not have gotten unregistered properly and it's a bug
            // in the unhandled oop generator.

        Since that condition must be rare, we can save considerable time not taking "pc" on every oop registration, with a minor (?) downside that we would not get the PC when unhandled oops detector is broken.

        Motivational example is the test that enters the registrator path very often:

        $ time CONF=linux-x86_64-server-fastdebug make run-test TEST=gc/epsilon/TestClasses.java TEST_VM_OPTS="-XX:+CheckUnhandledOops"

        Before:

        real 6m7.516s
        user 6m38.876s
        sys 0m4.566s

        After:

        real 2m33.344s
        user 3m4.788s
        sys 0m4.351s

        Tier1 also improves significantly:

        $ time CONF=linux-x86_64-server-fastdebug make run-test TEST=tier1 TEST_VM_OPTS="-XX:+CheckUnhandledOops"

        Before:

        real 60m43.022s
        user 1546m54.452s
        sys 45m0.769s

        After:

        real 42m59.204s
        user 1347m41.339s
        sys 50m43.837s

        For the reference, the baseline without CheckUnhandledOops enabled:

        $ time CONF=linux-x86_64-server-fastdebug make run-test TEST=tier1

        real 32m57.509s
        user 1230m5.149s
        sys 54m23.135s

        In other words, this cuts out about 2/3 of CheckUnhandledOops overhead.

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                Assignee:
                shade Aleksey Shipilev
                Reporter:
                shade Aleksey Shipilev
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