RFR(S): 8235673: [C1, C2] Split inlining control flags
Doerr, Martin
martin.doerr at sap.com
Fri May 8 12:56:01 UTC 2020
Hi Vladimir,
thanks a lot for looking at this, for finding the test issues and for reviewing the CSR.
For me, C2 is a fundamental part of the JVM. I would usually never build without it ��
(Except if we want to use C1 + GraalVM compiler only.)
But your right, --with-jvm-variants=client configuration should still be supported.
We can fix it by making the flags as obsolete if C2 is not included:
diff -r 5f5ed86d7883 src/hotspot/share/runtime/arguments.cpp
--- a/src/hotspot/share/runtime/arguments.cpp Fri May 08 11:14:28 2020 +0200
+++ b/src/hotspot/share/runtime/arguments.cpp Fri May 08 14:41:14 2020 +0200
@@ -562,6 +562,16 @@
{ "dup option", JDK_Version::jdk(9), JDK_Version::undefined(), JDK_Version::undefined() },
#endif
+#ifndef COMPILER2
+ // These flags were generally available, but are C2 only, now.
+ { "MaxInlineLevel", JDK_Version::undefined(), JDK_Version::jdk(15), JDK_Version::undefined() },
+ { "MaxRecursiveInlineLevel", JDK_Version::undefined(), JDK_Version::jdk(15), JDK_Version::undefined() },
+ { "InlineSmallCode", JDK_Version::undefined(), JDK_Version::jdk(15), JDK_Version::undefined() },
+ { "MaxInlineSize", JDK_Version::undefined(), JDK_Version::jdk(15), JDK_Version::undefined() },
+ { "FreqInlineSize", JDK_Version::undefined(), JDK_Version::jdk(15), JDK_Version::undefined() },
+ { "MaxTrivialSize", JDK_Version::undefined(), JDK_Version::jdk(15), JDK_Version::undefined() },
+#endif
+
{ NULL, JDK_Version(0), JDK_Version(0) }
};
This makes the VM accept the flags with warning:
jdk/bin/java -XX:MaxInlineLevel=9 -version
OpenJDK 64-Bit Client VM warning: Ignoring option MaxInlineLevel; support was removed in 15.0
If we do it this way, the only test which I think should get fixed is ReservedStackTest.
I think it should be sufficient to add -XX:C1MaxInlineLevel=2 in order to preserve the inlining behavior.
(TestStringIntrinsics2: C1 doesn't have String intrinsics anymore. compiler/c2 tests: Also written to test C2 specific things.)
What do you think?
Best regards,
Martin
> -----Original Message-----
> From: hotspot-compiler-dev <hotspot-compiler-dev-
> bounces at openjdk.java.net> On Behalf Of Vladimir Kozlov
> Sent: Donnerstag, 7. Mai 2020 19:11
> To: hotspot-compiler-dev at openjdk.java.net
> Subject: Re: RFR(S): 8235673: [C1, C2] Split inlining control flags
>
> I would suggest to build VM without C2 and run tests.
>
> I grepped tests with these flags I found next tests where we need to fix
> test's command (add
> -XX:+IgnoreUnrecognizedVMOptions) or add @requires
> vm.compiler2.enabled or duplicate test for C1 with corresponding C1
> flags (by ussing additional @test block).
>
> runtime/ReservedStack/ReservedStackTest.java
> compiler/intrinsics/string/TestStringIntrinsics2.java
> compiler/c2/Test6792161.java
> compiler/c2/Test5091921.java
>
> And there is issue with compiler/compilercontrol tests which use
> InlineSmallCode and I am not sure how to handle:
>
> http://hg.openjdk.java.net/jdk/jdk/file/55e9cb6b23ec/test/hotspot/jtreg/c
> ompiler/compilercontrol/share/scenario/Command.java#l36
>
> Thanks,
> Vladimir
>
> On 5/4/20 9:04 AM, Doerr, Martin wrote:
> > Hi Nils,
> >
> > thank you for looking at this and sorry for the late reply.
> >
> > I've added MaxTrivialSize and also updated the issue accordingly. Makes
> sense.
> > Do you have more flags in mind?
> >
> > Moving the flags which are only used by C2 into c2_globals definitely makes
> sense.
> >
> > Done in webrev.01:
> > http://cr.openjdk.java.net/~mdoerr/8235673_C1_inlining/webrev.01/
> >
> > Please take a look and let me know when my proposal is ready for a CSR.
> >
> > Best regards,
> > Martin
> >
> >
> >> -----Original Message-----
> >> From: hotspot-compiler-dev <hotspot-compiler-dev-
> >> bounces at openjdk.java.net> On Behalf Of Nils Eliasson
> >> Sent: Dienstag, 28. April 2020 18:29
> >> To: hotspot-compiler-dev at openjdk.java.net
> >> Subject: Re: RFR(S): 8235673: [C1, C2] Split inlining control flags
> >>
> >> Hi,
> >>
> >> Thanks for addressing this! This has been an annoyance for a long time.
> >>
> >> Have you though about including other flags - like MaxTrivialSize?
> >> MaxInlineSize is tested against it.
> >>
> >> Also - you should move the flags that are now c2-only to c2_globals.hpp.
> >>
> >> Best regards,
> >> Nils Eliasson
> >>
> >> On 2020-04-27 15:06, Doerr, Martin wrote:
> >>> Hi,
> >>>
> >>> while tuning inlining parameters for C2 compiler with JDK-8234863 we
> had
> >> discussed impact on C1.
> >>> I still think it's bad to share them between both compilers. We may want
> to
> >> do further C2 tuning without negative impact on C1 in the future.
> >>>
> >>> C1 has issues with substantial inlining because of the lack of uncommon
> >> traps. When C1 inlines a lot, stack frames may get large and code cache
> space
> >> may get wasted for cold or even never executed code. The situation gets
> >> worse when many patching stubs get used for such code.
> >>>
> >>> I had opened the following issue:
> >>> https://bugs.openjdk.java.net/browse/JDK-8235673
> >>>
> >>> And my initial proposal is here:
> >>> http://cr.openjdk.java.net/~mdoerr/8235673_C1_inlining/webrev.00/
> >>>
> >>>
> >>> Part of my proposal is to add an additional flag which I called
> >> C1InlineStackLimit to reduce stack utilization for C1 methods.
> >>> I have a simple example which shows wasted stack space (java example
> >> TestStack at the end).
> >>>
> >>> It simply counts stack frames until a stack overflow occurs. With the
> current
> >> implementation, only 1283 frames fit on the stack because the never
> >> executed method bogus_test with local variables gets inlined.
> >>> Reduced C1InlineStackLimit avoids inlining of bogus_test and we get
> 2310
> >> frames until stack overflow. (I only used C1 for this example. Can be
> >> reproduced as shown below.)
> >>>
> >>> I didn't notice any performance regression even with the aggressive
> setting
> >> of C1InlineStackLimit=5 with TieredCompilation.
> >>>
> >>> I know that I'll need a CSR for this change, but I'd like to get feedback in
> >> general and feedback about the flag names before creating a CSR.
> >>> I'd also be glad about feedback regarding the performance impact.
> >>>
> >>> Best regards,
> >>> Martin
> >>>
> >>>
> >>>
> >>> Command line:
> >>> jdk/bin/java -XX:TieredStopAtLevel=1 -XX:C1InlineStackLimit=20 -
> >> XX:C1MaxRecursiveInlineLevel=0 -Xss256k -Xbatch -XX:+PrintInlining -
> >> XX:CompileCommand=compileonly,TestStack::triggerStackOverflow
> >> TestStack
> >>> CompileCommand: compileonly TestStack.triggerStackOverflow
> >>> @ 8 TestStack::triggerStackOverflow (15 bytes)
> recursive
> >> inlining too deep
> >>> @ 11 TestStack::bogus_test (33 bytes) inline
> >>> caught java.lang.StackOverflowError
> >>> 1283 activations were on stack, sum = 0
> >>>
> >>> jdk/bin/java -XX:TieredStopAtLevel=1 -XX:C1InlineStackLimit=10 -
> >> XX:C1MaxRecursiveInlineLevel=0 -Xss256k -Xbatch -XX:+PrintInlining -
> >> XX:CompileCommand=compileonly,TestStack::triggerStackOverflow
> >> TestStack
> >>> CompileCommand: compileonly TestStack.triggerStackOverflow
> >>> @ 8 TestStack::triggerStackOverflow (15 bytes)
> recursive
> >> inlining too deep
> >>> @ 11 TestStack::bogus_test (33 bytes) callee uses too
> >> much stack
> >>> caught java.lang.StackOverflowError
> >>> 2310 activations were on stack, sum = 0
> >>>
> >>>
> >>> TestStack.java:
> >>> public class TestStack {
> >>>
> >>> static long cnt = 0,
> >>> sum = 0;
> >>>
> >>> public static void bogus_test() {
> >>> long c1 = 1, c2 = 2, c3 = 3, c4 = 4;
> >>> sum += c1 + c2 + c3 + c4;
> >>> }
> >>>
> >>> public static void triggerStackOverflow() {
> >>> cnt++;
> >>> triggerStackOverflow();
> >>> bogus_test();
> >>> }
> >>>
> >>>
> >>> public static void main(String args[]) {
> >>> try {
> >>> triggerStackOverflow();
> >>> } catch (StackOverflowError e) {
> >>> System.out.println("caught " + e);
> >>> }
> >>> System.out.println(cnt + " activations were on stack, sum = " +
> sum);
> >>> }
> >>> }
> >>>
> >
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