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8307766: Linux: Provide the option to override the timer slack
Reviewed-by: stuefe Backport-of: 7173c3009e0999f13eaa4bee5eedee7326f9d124
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3 files changed

+176
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3 files changed

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‎src/hotspot/os/linux/globals_linux.hpp

+13-1
Original file line numberDiff line numberDiff line change
@@ -77,7 +77,19 @@
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"Use CPU_ALLOC code path in os::active_processor_count ") \
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\
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product(bool, DumpPerfMapAtExit, false, DIAGNOSTIC, \
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"Write map file for Linux perf tool at exit")
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"Write map file for Linux perf tool at exit") \
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\
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product(intx, TimerSlack, -1, EXPERIMENTAL, \
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"Overrides the timer slack value to the given number of " \
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"nanoseconds. Lower value provides more accurate " \
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"high-precision timers, at the expense of (possibly) worse " \
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"power efficiency. In current Linux, 0 means using the " \
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"system-wide default, which would disable the override, but " \
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"VM would still print the current timer slack values. Use -1 "\
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"to disable both the override and the printouts." \
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"See prctl(PR_SET_TIMERSLACK) for more info.") \
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\
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// end of RUNTIME_OS_FLAGS
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‎src/hotspot/os/linux/os_linux.cpp

+20
Original file line numberDiff line numberDiff line change
@@ -113,6 +113,7 @@
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# include <inttypes.h>
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# include <sys/ioctl.h>
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# include <linux/elf-em.h>
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# include <sys/prctl.h>
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#ifdef __GLIBC__
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# include <malloc.h>
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#endif
@@ -967,6 +968,16 @@ bool os::create_thread(Thread* thread, ThreadType thr_type,
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if (ret == 0) {
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log_info(os, thread)("Thread \"%s\" started (pthread id: " UINTX_FORMAT ", attributes: %s). ",
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thread->name(), (uintx) tid, os::Posix::describe_pthread_attr(buf, sizeof(buf), &attr));
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// Print current timer slack if override is enabled and timer slack value is available.
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// Avoid calling prctl otherwise for extra safety.
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if (TimerSlack >= 0) {
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int slack = prctl(PR_GET_TIMERSLACK);
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if (slack >= 0) {
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log_info(os, thread)("Thread \"%s\" (pthread id: " UINTX_FORMAT ") timer slack: %dns",
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thread->name(), (uintx) tid, slack);
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}
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}
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} else {
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log_warning(os, thread)("Failed to start thread \"%s\" - pthread_create failed (%s) for attributes: %s.",
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thread->name(), os::errno_name(ret), os::Posix::describe_pthread_attr(buf, sizeof(buf), &attr));
@@ -4701,6 +4712,15 @@ jint os::init_2(void) {
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FLAG_SET_DEFAULT(UseCodeCacheFlushing, false);
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}
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// Override the timer slack value if needed. The adjustment for the main
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// thread will establish the setting for child threads, which would be
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// most threads in JDK/JVM.
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if (TimerSlack >= 0) {
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if (prctl(PR_SET_TIMERSLACK, TimerSlack) < 0) {
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vm_exit_during_initialization("Setting timer slack failed: %s", os::strerror(errno));
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}
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}
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return JNI_OK;
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}
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‎test/hotspot/jtreg/runtime/os/TestTimerSlack.java

+143
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,143 @@
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/*
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* Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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import java.util.regex.Pattern;
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import java.util.regex.Matcher;
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import jdk.test.lib.process.ProcessTools;
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import jdk.test.lib.process.OutputAnalyzer;
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/**
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* @test
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* @summary Check that timer slack options work
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* @requires os.family == "linux"
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* @requires vm.flagless
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* @library /test/lib
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* @run driver TestTimerSlack
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*/
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public class TestTimerSlack {
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public static void main(String[] args) throws Exception {
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int defaultSlack;
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// Check the timer slack value is not printed by default
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{
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ProcessBuilder pb = ProcessTools.createJavaProcessBuilder("-Xlog:os+thread",
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"TestTimerSlack$TestMain");
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OutputAnalyzer output = new OutputAnalyzer(pb.start());
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output.shouldHaveExitValue(0);
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output.shouldNotContain("timer slack:");
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}
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// Check the timer slack value is not printed when explicitly disabled
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{
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ProcessBuilder pb = ProcessTools.createJavaProcessBuilder("-Xlog:os+thread",
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"-XX:+UnlockExperimentalVMOptions",
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"-XX:TimerSlack=-1",
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"TestTimerSlack$TestMain");
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OutputAnalyzer output = new OutputAnalyzer(pb.start());
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output.shouldHaveExitValue(0);
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output.shouldNotContain("timer slack:");
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}
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// Check the timer slack value is good when system-wide default is requested
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{
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ProcessBuilder pb = ProcessTools.createJavaProcessBuilder("-Xlog:os+thread",
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"-XX:+UnlockExperimentalVMOptions",
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"-XX:TimerSlack=0",
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"TestTimerSlack$TestMain");
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OutputAnalyzer output = new OutputAnalyzer(pb.start());
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output.shouldHaveExitValue(0);
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output.shouldContain("timer slack:");
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defaultSlack = parseSlackValue(output);
77+
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if (defaultSlack == 0) {
79+
fail(output, "Default slack value (" + defaultSlack + ") is unexpected");
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}
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}
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// Check the timer slack value is accepted by all threads
84+
for (int slack : new int[] {1, 10, 100, 1000, 10000, 100000, 1000000}) {
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ProcessBuilder pb = ProcessTools.createJavaProcessBuilder("-Xlog:os+thread",
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"-XX:+UnlockExperimentalVMOptions",
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"-XX:TimerSlack=" + slack,
88+
"TestTimerSlack$TestMain");
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90+
OutputAnalyzer output = new OutputAnalyzer(pb.start());
91+
output.shouldHaveExitValue(0);
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output.shouldContain("timer slack:");
93+
94+
int actualSlack = parseSlackValue(output);
95+
if (actualSlack != slack) {
96+
fail(output, "Actual slack value (" + actualSlack + ") is not the requested one (" + slack + ")");
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}
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}
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}
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static final Pattern EXTRACT_PATTERN = Pattern.compile("(.*)timer slack: ([0-9]+)ns(.*)");
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public static int parseSlackValue(OutputAnalyzer output) {
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Integer value = null;
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for (String s : output.asLines()) {
106+
Matcher m = EXTRACT_PATTERN.matcher(s);
107+
if (m.matches()) {
108+
Integer parsedValue = Integer.parseInt(m.group(2));
109+
if (value == null) {
110+
value = parsedValue;
111+
} else if (!value.equals(parsedValue)) {
112+
fail(output, "Multiple timer slack values detected");
113+
}
114+
}
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}
116+
if (value == null) {
117+
fail(output, "No timer slack values detected");
118+
}
119+
return value;
120+
}
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122+
private static void fail(OutputAnalyzer output, String msg) {
123+
output.reportDiagnosticSummary();
124+
throw new IllegalStateException(msg);
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}
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public static class TestMain {
128+
static final int THREADS = 8;
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130+
public static void main(String... args) throws Exception {
131+
Thread[] ts = new Thread[THREADS];
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for (int c = 0; c < THREADS; c++) {
133+
ts[c] = new Thread();
134+
ts[c].start();
135+
}
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137+
for (int c = 0; c < THREADS; c++) {
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ts[c].join();
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}
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}
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}
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}

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