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8307766: Linux: Provide the option to override the timer slack

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Reviewed-by: dholmes, stuefe
This commit is contained in:
Aleksey Shipilev 2023-07-06 10:38:34 +00:00
parent 356067d03f
commit 7173c3009e
3 changed files with 176 additions and 1 deletions
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14
src/hotspot/os/linux/globals_linux.hpp
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@ -77,7 +77,19 @@
"Use CPU_ALLOC code path in os::active_processor_count ") \
\
product(bool, DumpPerfMapAtExit, false, DIAGNOSTIC, \
"Write map file for Linux perf tool at exit")
"Write map file for Linux perf tool at exit") \
\
product(intx, TimerSlack, -1, EXPERIMENTAL, \
"Overrides the timer slack value to the given number of " \
"nanoseconds. Lower value provides more accurate " \
"high-precision timers, at the expense of (possibly) worse " \
"power efficiency. In current Linux, 0 means using the " \
"system-wide default, which would disable the override, but " \
"VM would still print the current timer slack values. Use -1 "\
"to disable both the override and the printouts." \
"See prctl(PR_SET_TIMERSLACK) for more info.") \
\
// end of RUNTIME_OS_FLAGS

20
src/hotspot/os/linux/os_linux.cpp
View File

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

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