RFR: 8344232: [PPC64] secondary_super_cache does not scale well: C1 and interpreter

[Richard Reingruber]

On Wed, 22 Jan 2025 12:21:54 GMT, Richard Reingruber <rrich at openjdk.org> wrote:

>> PPC64 implementation of https://github.com/openjdk/jdk/commit/ead0116f2624e0e34529e47e4f509142d588b994. I have implemented a couple of rotate instructions.
>> The first commit only implements `lookup_secondary_supers_table_var` and uses it in C2. The second commit makes the changes to use it in the interpreter, runtime and C1.
>> C1 part is refactored such that the same code as before this patch is generated when `UseSecondarySupersTable` is disabled. Some stubs are modified to provide one more temp register.
>> 
>> Performance difference can be observed when C2 is disabled (measured on Power10):
>> 
>> 
>> -XX:TieredStopAtLevel=1 -XX:-UseSecondarySupersTable:
>> SecondarySuperCacheHits.test  avgt   15  13.028 ± 0.005  ns/op
>> SecondarySuperCacheInterContention.test     avgt   15  417.746 ± 19.046  ns/op
>> SecondarySuperCacheInterContention.test:t1  avgt   15  417.852 ± 17.814  ns/op
>> SecondarySuperCacheInterContention.test:t2  avgt   15  417.641 ± 23.431  ns/op
>> SecondarySuperCacheIntraContention.test  avgt   15  340.995 ± 5.620  ns/op
>> 
>> 
>> 
>> -XX:TieredStopAtLevel=1 -XX:+UseSecondarySupersTable:
>> SecondarySuperCacheHits.test  avgt   15  14.539 ± 0.002  ns/op
>> SecondarySuperCacheInterContention.test     avgt   15  25.667 ± 0.576  ns/op
>> SecondarySuperCacheInterContention.test:t1  avgt   15  25.709 ± 0.655  ns/op
>> SecondarySuperCacheInterContention.test:t2  avgt   15  25.626 ± 0.820  ns/op
>> SecondarySuperCacheIntraContention.test  avgt   15  22.466 ± 1.554  ns/op
>> 
>> 
>> `SecondarySuperCacheHits` seems to be slightly slower, but `SecondarySuperCacheInterContention` and `SecondarySuperCacheIntraContention` are much faster (when C2 is disabled).
>
> src/hotspot/cpu/ppc/macroAssembler_ppc.cpp line 2157:
> 
>> 2155: 
>> 2156:   bind(fallthru);
>> 2157:   if (L_success != nullptr && result_reg == noreg) {
> 
> Is there a problem if `L_success == nullptr && result_reg == noreg` and there aren't any secondary supers?
> In that case we would reach here with CR0.eq from L2134 and we would fallthrough with CR0.eq. Due to the change in `C1StubId::slow_subtype_check_id` we would return there with CR0.eq.

This is a reproducer:

public class InstanceOfTest {

    public static interface TestInterfaceI {
    }

    public static class TestClassNegative {
    }

    public static void main(String[] args) {
        Object obj = new TestClassNegative();
        for (int i = 100_000; i > 0; i--) {
            dontinline_testMethod(obj);
        }
        boolean result = dontinline_testMethod(obj);
        System.out.println("result: " + result);
    }

    static boolean dontinline_testMethod(Object obj) {
        return obj instanceof TestInterfaceI;
    }
}


./jdk/bin/java -XX:TieredStopAtLevel=1 -XX:-UseSecondarySupersTable InstanceOfTest
result: true

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/22881#discussion_r1925725737