RFR(S): 8235673: [C1, C2] Split inlining control flags
Doerr, Martin
martin.doerr at sap.com
Fri May 8 21:06:40 UTC 2020
Hi Vladimir,
> You need update your CSR - add information about this and above code change. Example:
> https://bugs.openjdk.java.net/browse/JDK-8238840
I've updated the CSR with obsolete and expired flags as in the example.
> I would suggest to fix tests anyway (there are only few) because new
> warning output could be unexpected.
Ok. I'll prepare a webrev with fixed tests.
Best regards,
Martin
> -----Original Message-----
> From: Vladimir Kozlov <vladimir.kozlov at oracle.com>
> Sent: Freitag, 8. Mai 2020 21:43
> To: Doerr, Martin <martin.doerr at sap.com>; hotspot-compiler-
> dev at openjdk.java.net
> Subject: Re: RFR(S): 8235673: [C1, C2] Split inlining control flags
>
> Hi Martin
>
> On 5/8/20 5:56 AM, Doerr, Martin wrote:
> > 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.)
>
> Yes it is one of cases.
>
> > But your right, --with-jvm-variants=client configuration should still be
> supported.
>
> Yes.
>
> >
> > 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) }
> > };
>
> Right. I think you should do full process for these product flags deprecation
> with obsoleting in JDK 16 for VM builds
> which do not include C2. You need update your CSR - add information about
> this and above code change. Example:
>
> https://bugs.openjdk.java.net/browse/JDK-8238840
>
> >
> > 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?
>
> I would suggest to fix tests anyway (there are only few) because new
> warning output could be unexpected.
> And it will be future-proof when warning will be converted into error
> (if/when C2 goes away).
>
> Thanks,
> Vladimir
>
> >
> > 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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