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Further reduce ensureAccessible() overhead (#8895)

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Motivation:

This PR fixes some non-negligible overhead discovered in the ByteBuf
accessibility (non-zero refcount) checking. The cause turned out to be
mostly twofold:
- Unnecessary operations used to calculate the refcount from the "raw"
encoded int field value
- Call stack depths exceeding the default limit for inlining, in some
places (CompositeByteBuf in particular)

It's a follow-on from #8882 which uses the maxCapacity field for a
simpler non-negative check. The performance gap between these two
variants appears to be _mostly_ closed, but there's one exception which
may warrant further analysis.

Modifications:

- Replace ABB.internalRefCount() with ByteBuf.isAccessible(), the
default still checks for non-zero refCnt()
- Just test for parity of raw refCnt instead of converting to "real",
with fast-path for specific small values
- Make sure isAccessible() is delegated by derived/wrapper ByteBufs
- Use existing freed flag in CompositeByteBuf for faster isAccessible()
- Manually inline some calls in methods like CompositeByteBuf.setLong()
and AbstractReferenceCountedByteBuf.isAccessible() to reduce stack
depths (to ensure default inlining limit isn't hit)
- Add ByteBufAccessBenchmark which is an extension of
UnsafeByteBufBenchmark (maybe latter could now be removed)

Results:

Before:

Benchmark   (bufferType)  (checkAccessible)  (checkBounds)   Mode  Cnt
Score          Error  Units
readBatch         UNSAFE               true           true  thrpt   30
84524972.863 ±   518338.811  ops/s
readBatch   UNSAFE_SLICE               true           true  thrpt   30
38608795.037 ±   298176.974  ops/s
readBatch           HEAP               true           true  thrpt   30
80003697.649 ±   974674.119  ops/s
readBatch      COMPOSITE               true           true  thrpt   30
18495554.788 ±   108075.023  ops/s
setGetLong        UNSAFE               true           true  thrpt   30
247069881.578 ± 10839162.593  ops/s
setGetLong  UNSAFE_SLICE               true           true  thrpt   30
196355905.206 ±  1802420.990  ops/s
setGetLong          HEAP               true           true  thrpt   30
245686644.713 ± 11769311.527  ops/s
setGetLong     COMPOSITE               true           true  thrpt   30
83170940.687 ±   657524.123  ops/s
setLong           UNSAFE               true           true  thrpt   30
278940253.918 ±  1807265.259  ops/s
setLong     UNSAFE_SLICE               true           true  thrpt   30
202556738.764 ± 11887973.563  ops/s
setLong             HEAP               true           true  thrpt   30
280045958.053 ±  2719583.400  ops/s
setLong        COMPOSITE               true           true  thrpt   30
121299806.002 ±  2155084.707  ops/s


After:

Benchmark   (bufferType)  (checkAccessible)  (checkBounds)   Mode  Cnt
Score          Error  Units
readBatch         UNSAFE               true           true  thrpt   30
101641801.035 ±  3950050.059  ops/s
readBatch   UNSAFE_SLICE               true           true  thrpt   30
84395902.846 ±  4339579.057  ops/s
readBatch           HEAP               true           true  thrpt   30
100179060.207 ±  3222487.287  ops/s
readBatch      COMPOSITE               true           true  thrpt   30
42288494.472 ±   294919.633  ops/s
setGetLong        UNSAFE               true           true  thrpt   30
304530755.027 ±  6574163.899  ops/s
setGetLong  UNSAFE_SLICE               true           true  thrpt   30
212028547.645 ± 14277828.768  ops/s
setGetLong          HEAP               true           true  thrpt   30
309335422.609 ±  2272150.415  ops/s
setGetLong     COMPOSITE               true           true  thrpt   30
160383609.236 ±   966484.033  ops/s
setLong           UNSAFE               true           true  thrpt   30
298055969.747 ±  7437449.627  ops/s
setLong     UNSAFE_SLICE               true           true  thrpt   30
223784178.650 ±  9869750.095  ops/s
setLong             HEAP               true           true  thrpt   30
302543263.328 ±  8140104.706  ops/s
setLong        COMPOSITE               true           true  thrpt   30
157083673.285 ±  3528779.522  ops/s

There's also a similar knock-on improvement to other benchmarks (e.g.
HPACK encoding/decoding) as shown in #8882.

For sanity I did a final comparison of the "fast path" tweak using one
of the HPACK benchmarks:

(rawCnt & 1) == 0:

Benchmark                     (limitToAscii)  (sensitive)  (size)   Mode
Cnt      Score     Error  Units
HpackDecoderBenchmark.decode            true         true  MEDIUM  thrpt
30  50914.479 ± 940.114  ops/s


rawCnt == 2 || rawCnt == 4 || rawCnt == 6 || rawCnt == 8 ||  (rawCnt &
1) == 0:

Benchmark                     (limitToAscii)  (sensitive)  (size)   Mode
Cnt      Score      Error  Units
HpackDecoderBenchmark.decode            true         true  MEDIUM  thrpt
30  60036.425 ± 1478.196  ops/s
This commit is contained in:
Nick Hill 2019-02-28 11:40:42 -08:00 committed by Norman Maurer
parent 625c4e8286
commit 0811409ca3
9 changed files with 209 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
buffer/src/main/java/io/netty/buffer/AbstractByteBuf.java
View File

@ -1437,19 +1437,11 @@ public abstract class AbstractByteBuf extends ByteBuf {
* if the buffer was released before.
*/
protected final void ensureAccessible() {
if (checkAccessible && internalRefCnt() == 0) {
if (checkAccessible && !isAccessible()) {
throw new IllegalReferenceCountException(0);
}
}
/**
* Returns the reference count that is used internally by {@link #ensureAccessible()} to try to guard
* against using the buffer after it was released (best-effort).
*/
int internalRefCnt() {
return refCnt();
}
final void setIndex0(int readerIndex, int writerIndex) {
this.readerIndex = readerIndex;
this.writerIndex = writerIndex;

5
buffer/src/main/java/io/netty/buffer/AbstractDerivedByteBuf.java
View File

@ -31,6 +31,11 @@ public abstract class AbstractDerivedByteBuf extends AbstractByteBuf {
super(maxCapacity);
}
@Override
final boolean isAccessible() {
return unwrap().isAccessible();
}
@Override
public final int refCnt() {
return refCnt0();

13
buffer/src/main/java/io/netty/buffer/AbstractReferenceCountedByteBuf.java
View File

@ -64,10 +64,19 @@ public abstract class AbstractReferenceCountedByteBuf extends AbstractByteBuf {
}
@Override
int internalRefCnt() {
boolean isAccessible() {
// Try to do non-volatile read for performance as the ensureAccessible() is racy anyway and only provide
// a best-effort guard.
return realRefCnt(nonVolatileRawCnt());
// This is copied explicitly from the nonVolatileRawCnt() method above to reduce call stack depth,
// to avoid hitting the default limit for inlining (9)
final int rawCnt = REFCNT_FIELD_OFFSET != -1 ? PlatformDependent.getInt(this, REFCNT_FIELD_OFFSET)
: refCntUpdater.get(this);
// The "real" ref count is > 0 if the rawCnt is even.
// (x & y) appears to be surprisingly expensive relative to (x == y). Thus the expression below provides
// a fast path for most common cases where the ref count is 1, 2, 3 or 4.
return rawCnt == 2 || rawCnt == 4 || rawCnt == 6 || rawCnt == 8 || (rawCnt & 1) == 0;
}
@Override

8
buffer/src/main/java/io/netty/buffer/ByteBuf.java
View File

@ -2445,4 +2445,12 @@ public abstract class ByteBuf implements ReferenceCounted, Comparable<ByteBuf> {
@Override
public abstract ByteBuf touch(Object hint);
/**
* Used internally by {@link AbstractByteBuf#ensureAccessible()} to try to guard
* against using the buffer after it was released (best-effort).
*/
boolean isAccessible() {
return refCnt() != 0;
}
}

22
buffer/src/main/java/io/netty/buffer/CompositeByteBuf.java
View File

@ -300,7 +300,7 @@ public class CompositeByteBuf extends AbstractReferenceCountedByteBuf implements
@SuppressWarnings("deprecation")
private Component newComponent(ByteBuf buf, int offset) {
if (checkAccessible && buf.refCnt() == 0) {
if (checkAccessible && !buf.isAccessible()) {
throw new IllegalReferenceCountException(0);
}
int srcIndex = buf.readerIndex(), len = buf.readableBytes();
@ -1074,7 +1074,8 @@ public class CompositeByteBuf extends AbstractReferenceCountedByteBuf implements
@Override
public CompositeByteBuf setShort(int index, int value) {
super.setShort(index, value);
checkIndex(index, 2);
_setShort(index, value);
return this;
}
@ -1108,7 +1109,8 @@ public class CompositeByteBuf extends AbstractReferenceCountedByteBuf implements
@Override
public CompositeByteBuf setMedium(int index, int value) {
super.setMedium(index, value);
checkIndex(index, 3);
_setMedium(index, value);
return this;
}
@ -1142,7 +1144,8 @@ public class CompositeByteBuf extends AbstractReferenceCountedByteBuf implements
@Override
public CompositeByteBuf setInt(int index, int value) {
super.setInt(index, value);
checkIndex(index, 4);
_setInt(index, value);
return this;
}
@ -1176,7 +1179,8 @@ public class CompositeByteBuf extends AbstractReferenceCountedByteBuf implements
@Override
public CompositeByteBuf setLong(int index, long value) {
super.setLong(index, value);
checkIndex(index, 8);
_setLong(index, value);
return this;
}
@ -1284,7 +1288,6 @@ public class CompositeByteBuf extends AbstractReferenceCountedByteBuf implements
int i = toComponentIndex0(index);
int readBytes = 0;
do {
Component c = components[i];
int localLength = Math.min(length, c.endOffset - index);
@ -2052,7 +2055,7 @@ public class CompositeByteBuf extends AbstractReferenceCountedByteBuf implements
@Override
public CompositeByteBuf writeBytes(byte[] src) {
writeBytes(src, 0, src.length);
super.writeBytes(src, 0, src.length);
return this;
}
@ -2120,6 +2123,11 @@ public class CompositeByteBuf extends AbstractReferenceCountedByteBuf implements
}
}
@Override
boolean isAccessible() {
return !freed;
}
@Override
public ByteBuf unwrap() {
return null;

5
buffer/src/main/java/io/netty/buffer/SwappedByteBuf.java
View File

@ -997,6 +997,11 @@ public class SwappedByteBuf extends ByteBuf {
return buf.refCnt();
}
@Override
final boolean isAccessible() {
return buf.isAccessible();
}
@Override
public ByteBuf retain() {
buf.retain();

5
buffer/src/main/java/io/netty/buffer/WrappedByteBuf.java
View File

@ -1033,4 +1033,9 @@ class WrappedByteBuf extends ByteBuf {
public boolean release(int decrement) {
return buf.release(decrement);
}
@Override
final boolean isAccessible() {
return buf.isAccessible();
}
}

4
buffer/src/main/java/io/netty/buffer/WrappedCompositeByteBuf.java
View File

@ -424,8 +424,8 @@ class WrappedCompositeByteBuf extends CompositeByteBuf {
}
@Override
int internalRefCnt() {
return wrapped.internalRefCnt();
final boolean isAccessible() {
return wrapped.isAccessible();
}
@Override

157
microbench/src/main/java/io/netty/buffer/ByteBufAccessBenchmark.java Normal file
View File

@ -0,0 +1,157 @@
/*
* Copyright 2019 The Netty Project
*
* The Netty Project licenses this file to you under the Apache License,
* version 2.0 (the "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*/
package io.netty.buffer;
import java.nio.ByteBuffer;
import java.util.concurrent.TimeUnit;
import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Fork;
import org.openjdk.jmh.annotations.Measurement;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Param;
import org.openjdk.jmh.annotations.Setup;
import org.openjdk.jmh.annotations.TearDown;
import org.openjdk.jmh.annotations.Warmup;
import io.netty.microbench.util.AbstractMicrobenchmark;
import io.netty.util.internal.PlatformDependent;
@Warmup(iterations = 5, time = 1500, timeUnit = TimeUnit.MILLISECONDS)
@Measurement(iterations = 10, time = 1500, timeUnit = TimeUnit.MILLISECONDS)
@Fork(3)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public class ByteBufAccessBenchmark extends AbstractMicrobenchmark {
static final class NioFacade extends WrappedByteBuf {
private final ByteBuffer byteBuffer;
NioFacade(ByteBuffer byteBuffer) {
super(Unpooled.EMPTY_BUFFER);
this.byteBuffer = byteBuffer;
}
@Override
public ByteBuf setLong(int index, long value) {
byteBuffer.putLong(index, value);
return this;
}
@Override
public long getLong(int index) {
return byteBuffer.getLong(index);
}
@Override
public byte readByte() {
return byteBuffer.get();
}
@Override
public ByteBuf touch() {
// hack since WrappedByteBuf.readerIndex(int) is final
byteBuffer.position(0);
return this;
}
@Override
public boolean release() {
PlatformDependent.freeDirectBuffer(byteBuffer);
return true;
}
}
public enum ByteBufType {
UNSAFE {
@Override
ByteBuf newBuffer() {
return new UnpooledUnsafeDirectByteBuf(
UnpooledByteBufAllocator.DEFAULT, 64, 64).setIndex(0, 64);
}
},
UNSAFE_SLICE {
@Override
ByteBuf newBuffer() {
return UNSAFE.newBuffer().slice(16, 48);
}
},
HEAP {
@Override
ByteBuf newBuffer() {
return new UnpooledUnsafeHeapByteBuf(
UnpooledByteBufAllocator.DEFAULT, 64, 64).setIndex(0, 64);
}
},
COMPOSITE {
@Override
ByteBuf newBuffer() {
return Unpooled.wrappedBuffer(UNSAFE.newBuffer(), HEAP.newBuffer());
}
},
NIO {
@Override
ByteBuf newBuffer() {
return new NioFacade(ByteBuffer.allocateDirect(64));
}
};
abstract ByteBuf newBuffer();
}
@Param
public ByteBufType bufferType;
@Param({ "true", "false" })
public String checkAccessible;
@Param({ "true", "false" })
public String checkBounds;
@Param({ "8" })
public int batchSize; // applies only to readBatch benchmark
@Setup
public void setup() {
System.setProperty("io.netty.buffer.checkAccessible", checkAccessible);
System.setProperty("io.netty.buffer.checkBounds", checkBounds);
buffer = bufferType.newBuffer();
}
private ByteBuf buffer;
@TearDown
public void tearDown() {
buffer.release();
System.clearProperty("io.netty.buffer.checkAccessible");
System.clearProperty("io.netty.buffer.checkBounds");
}
@Benchmark
public long setGetLong() {
return buffer.setLong(0, 1).getLong(0);
}
@Benchmark
public ByteBuf setLong() {
return buffer.setLong(0, 1);
}
@Benchmark
public int readBatch() {
buffer.readerIndex(0).touch();
int result = 0;
for (int i = 0, size = batchSize; i < size; i++) {
result += buffer.readByte();
}
return result;
}
}