Hello,
As it's been quite a while already, I wanted to nudge this RFR forward. Who
would be best qualified to review this PR?
Thank you!
Ludovic
On Wed, Aug 18, 2021 at 9:21 PM Marcus Hirt <h...@openjdk.java.net> wrote:
> On Mon, 19 Jul 2021 09:25:59 GMT, Ludovic Henry <luhe...@openjdk.org>
> wrote:
>
> >> When the signal sent for AsyncGetCallTrace or JFR would land on a
> runtime stub (like arraycopy), a vtable stub, or the prolog of a compiled
> method, it wouldn't be able to detect the sender (caller) frame for
> multiple reasons. This patch fixes these cases through adding
> CodeBlob-specific frame parser which are in the best position to know how a
> frame is setup.
> >>
> >> The following examples have been profiled with honest-profiler which
> uses `AsyncGetCallTrace`.
> >>
> >> # `Prof1`
> >>
> >> 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());
> >> }
> >> }
> >>
> >>
> >> - 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
> >>
> >>
> >> # `Prof2`
> >>
> >> 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();
> >> }
> >> }
> >> }
> >>
> >>
> >> - 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 `VtableBlob::FrameParser` and `nmethod::FrameParser`:
> >>
> >> 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]
> >
> > 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.
>
> Ok. Do you know who should be the primary reviewer? Rickard Bäckman? Nils
> Eliasson?
>
> -------------
>
> PR: https://git.openjdk.java.net/jdk/pull/4436
>
