On Mon, 23 Aug 2021 10:28:36 GMT, Jaroslav Bachorik <jbacho...@openjdk.org> wrote:
>> Ludovic Henry has updated the pull request with a new target base due to a >> merge or a rebase. The incremental webrev excludes the unrelated changes >> brought in by the merge/rebase. The pull request contains eight additional >> commits since the last revision: >> >> - Remove FrameParser and the required allocation >> >> The need for the allocation would be it non async-safe. However, >> AsyncGetCallTrace is async-safe and thus can't allow for allocations. >> - Merge branch 'master' of https://github.com/openjdk/jdk into fix-8178287 >> - Fix comments >> - Disable checks in FrameParser when known to be safe >> - Allow AsyncGetCallTrace and JFR to unwind stack from vtable stub >> >> The program is the following: >> >> ``` >> import java.util.function.Supplier; >> >> public class Prof2 { >> >> public static void main(String[] args) { >> var rand = new java.util.Random(0); >> Supplier[] suppliers = { >> () -> 0, >> () -> 1, >> () -> 2, >> () -> 3, >> }; >> >> long sum = 0; >> for (int i = 0; i >= 0; i++) { >> sum += (int)suppliers[i % suppliers.length].get(); >> } >> } >> } >> ``` >> >> The results are as follows: >> >> - Baseline (from previous commit): >> >> Flat Profile (by method): >> (t 39.3,s 39.3) AGCT::Unknown Java[ERR=-5] >> (t 40.3,s 36.1) Prof2::main >> (t 6.4,s 5.3) Prof2$$Lambda$28.0x0000000800081000::get >> (t 6.1,s 5.1) Prof2$$Lambda$29.0x0000000800081220::get >> (t 6.0,s 5.0) Prof2$$Lambda$27.0x0000000800080c28::get >> (t 6.1,s 5.0) Prof2$$Lambda$26.0x0000000800080a08::get >> (t 1.1,s 1.1) Prof2::lambda$main$2 >> (t 1.1,s 1.1) Prof2::lambda$main$0 >> (t 1.0,s 1.0) Prof2::lambda$main$1 >> (t 0.9,s 0.9) Prof2::lambda$main$3 >> (t 0.1,s 0.1) AGCT::Unknown not Java[ERR=-3] >> >> - With unwind from vtable stub >> >> Flat Profile (by method): >> (t 74.1,s 70.3) Prof2::main >> (t 6.5,s 5.5) Prof2$$Lambda$29.0x0000000800081220::get >> (t 6.6,s 5.4) Prof2$$Lambda$28.0x0000000800081000::get >> (t 5.7,s 5.0) Prof2$$Lambda$26.0x0000000800080a08::get >> (t 5.9,s 5.0) Prof2$$Lambda$27.0x0000000800080c28::get >> (t 4.9,s 4.9) AGCT::Unknown Java[ERR=-5] >> (t 1.2,s 1.2) Prof2::lambda$main$2 >> (t 0.9,s 0.9) Prof2::lambda$main$3 >> (t 0.9,s 0.9) Prof2::lambda$main$1 >> (t 0.7,s 0.7) Prof2::lambda$main$0 >> (t 0.1,s 0.1) AGCT::Unknown not Java[ERR=-3] >> >> We attribute the vtable stub to the caller and not the callee, which is >> already an improvement from the existing case. >> - Allow AsyncGetCallTrace and JFR to unwind stack from nmethod's prolog >> >> When sampling hits the prolog of a method, Hotspot assumes it's unable >> to parse the frame. This change allows to parse such frame on x86 by >> specializing which instruction it's hitting in the prolog. >> >> The results are as follows: >> >> - Baseline: >> >> Flat Profile (by method): >> (t 60.7,s 60.7) AGCT::Unknown Java[ERR=-5] >> (t 39.2,s 35.2) Prof2::main >> (t 1.4,s 1.4) Prof2::lambda$main$3 >> (t 1.0,s 1.0) Prof2::lambda$main$2 >> (t 0.9,s 0.9) Prof2::lambda$main$1 >> (t 0.7,s 0.7) Prof2::lambda$main$0 >> (t 0.1,s 0.1) AGCT::Unknown not Java[ERR=-3] >> (t 0.0,s 0.0) java.lang.Thread::exit >> (t 0.9,s 0.0) Prof2$$Lambda$2.0x0000000800c00c28::get >> (t 1.0,s 0.0) Prof2$$Lambda$3.0x0000000800c01000::get >> (t 1.4,s 0.0) Prof2$$Lambda$4.0x0000000800c01220::get >> (t 0.7,s 0.0) Prof2$$Lambda$1.0x0000000800c00a08::get >> >> - With incomplete frame parsing: >> >> Flat Profile (by method): >> (t 39.3,s 39.3) AGCT::Unknown Java[ERR=-5] >> (t 40.3,s 36.1) Prof2::main >> (t 6.4,s 5.3) Prof2$$Lambda$28.0x0000000800081000::get >> (t 6.1,s 5.1) Prof2$$Lambda$29.0x0000000800081220::get >> (t 6.0,s 5.0) Prof2$$Lambda$27.0x0000000800080c28::get >> (t 6.1,s 5.0) Prof2$$Lambda$26.0x0000000800080a08::get >> (t 1.1,s 1.1) Prof2::lambda$main$2 >> (t 1.1,s 1.1) Prof2::lambda$main$0 >> (t 1.0,s 1.0) Prof2::lambda$main$1 >> (t 0.9,s 0.9) Prof2::lambda$main$3 >> (t 0.1,s 0.1) AGCT::Unknown not Java[ERR=-3] >> (t 0.0,s 0.0) java.util.Locale::getInstance >> (t 0.0,s 0.0) AGCT::Not walkable Java[ERR=-6] >> (t 0.0,s 0.0) >> jdk.internal.loader.BuiltinClassLoader::loadClassOrNull >> (t 0.0,s 0.0) java.lang.ClassLoader::loadClass >> (t 0.0,s 0.0) sun.net.util.URLUtil::urlNoFragString >> (t 0.0,s 0.0) java.lang.Class::forName0 >> (t 0.0,s 0.0) java.util.Locale::initDefault >> (t 0.0,s 0.0) jdk.internal.loader.BuiltinClassLoader::loadClass >> (t 0.0,s 0.0) jdk.internal.loader.URLClassPath::getLoader >> (t 0.0,s 0.0) jdk.internal.loader.URLClassPath::getResource >> (t 0.0,s 0.0) java.lang.String::toLowerCase >> (t 0.0,s 0.0) sun.launcher.LauncherHelper::loadMainClass >> (t 0.0,s 0.0) sun.launcher.LauncherHelper::checkAndLoadMain >> (t 0.0,s 0.0) java.util.Locale::<clinit> >> (t 0.0,s 0.0) >> jdk.internal.loader.BuiltinClassLoader::findClassOnClassPathOrNull >> (t 0.0,s 0.0) >> jdk.internal.loader.ClassLoaders$AppClassLoader::loadClass >> (t 0.0,s 0.0) java.lang.Class::forName >> >> The program is as follows: >> >> ``` >> import java.util.function.Supplier; >> >> public class Prof2 { >> >> public static void main(String[] args) { >> var rand = new java.util.Random(0); >> Supplier[] suppliers = { >> () -> 0, >> () -> 1, >> () -> 2, >> () -> 3, >> }; >> >> long sum = 0; >> for (int i = 0; i >= 0; i++) { >> sum += (int)suppliers[i % suppliers.length].get(); >> } >> } >> } >> ``` >> >> We see that the results are particularely useful in this case as the >> methods are very short (it only returns an integer), and the probability >> of hitting the prolog is then very high. >> - Allow AsyncGetCallTrace and JFR to walk a stub frame >> >> When the signal sent for AsyncGetCallTrace or JFR would land on a stub >> (like arraycopy), it wouldn't be able to detect the sender (caller) >> frame because `_cb->frame_size() == 0`. >> >> Because we fully control how the prolog and epilog of stub code is >> generated, we know there are two cases: >> 1. A stack frame is allocated via macroAssembler->enter(), and consists >> in `push rbp; mov rsp, rbp;`. >> 2. No stack frames are allocated and rbp is left unchanged and rsp is >> decremented with the `call` instruction that push the return `pc` on the >> stack. >> >> For case 1., we can easily know the sender frame by simply looking at >> rbp, especially since we know that all stubs preserve the frame pointer >> (on x86 at least). >> >> For case 2., we end up returning the sender's sender, but that already >> gives us more information than what we have today. >> >> The results are as follows: >> >> - Baseline: >> >> Flat Profile (by method): >> (t 99.4,s 99.4) AGCT::Unknown Java[ERR=-5] >> (t 0.5,s 0.2) Prof1::main >> (t 0.2,s 0.2) java.lang.AbstractStringBuilder::append >> (t 0.1,s 0.1) AGCT::Unknown not Java[ERR=-3] >> (t 0.0,s 0.0) >> java.lang.AbstractStringBuilder::ensureCapacityInternal >> (t 0.0,s 0.0) java.lang.AbstractStringBuilder::shift >> (t 0.0,s 0.0) java.lang.String::getBytes >> (t 0.0,s 0.0) java.lang.AbstractStringBuilder::putStringAt >> (t 0.0,s 0.0) java.lang.StringBuilder::delete >> (t 0.2,s 0.0) java.lang.StringBuilder::append >> (t 0.0,s 0.0) java.lang.AbstractStringBuilder::delete >> (t 0.0,s 0.0) java.lang.AbstractStringBuilder::putStringAt >> >> - With StubRoutinesBlob::FrameParser >> >> Flat Profile (by method): >> (t 98.7,s 98.7) >> java.lang.AbstractStringBuilder::ensureCapacityInternal >> (t 0.9,s 0.9) java.lang.AbstractStringBuilder::delete >> (t 99.8,s 0.2) Prof1::main >> (t 0.1,s 0.1) AGCT::Unknown not Java[ERR=-3] >> (t 0.0,s 0.0) AGCT::Unknown Java[ERR=-5] >> (t 98.8,s 0.0) java.lang.AbstractStringBuilder::append >> (t 98.8,s 0.0) java.lang.StringBuilder::append >> (t 0.9,s 0.0) java.lang.StringBuilder::delete >> >> The program is as follows: >> >> ``` >> public class Prof1 { >> >> public static void main(String[] args) { >> StringBuilder sb = new StringBuilder(); >> for (int i = 0; i < 1000000; i++) { >> sb.append("ab"); >> sb.delete(0, 1); >> } >> System.out.println(sb.length()); >> } >> } >> ``` >> >> We now account for the arraycopy stub which is called by >> AbstractStringBuilder::ensureCapacityInternal. It was previously ignored >> because it would not know how to parse the frame for the arraycopy stub >> and would fall in the AGCT::Unknown Java[ERR=-5] section. >> >> However, it still isn't perfect since it doesn't point to the arraycopy >> stub >> directly. >> - Extract sender frame parsing to CodeBlock::FrameParser >> >> Whether and how a frame is setup is controlled by the code generator >> for the specific CodeBlock. The CodeBlock is then in the best place to >> know how >> to parse the sender's frame from the current frame in the given CodeBlock. >> >> This refactoring proposes to extract this parsing out of `frame` and into >> a >> `CodeBlock::FrameParser`. This FrameParser is then specialized in the >> relevant >> inherited children of CodeBlock. >> >> This change is to largely facilitate adding new supported cases for >> JDK-8252417 >> like runtime stubs. > > @dcubed-ojdk , @dholmes-ora would you be willing/able to take a look at this > change, pretty please? Sorry @jbachorik but frames and code-blobs are not an area I know. David ------------- PR: https://git.openjdk.java.net/jdk/pull/4436
