Linux 实时性能测试工具——Cyclictest 的使用与分析

Linux 实时性能测试工具——Cyclictest 的使用与分析

关于Cyclictest工具，在Wiki上有说明：​​is a high resolution test program, written by User:Tglx, maintained by Clark Williams and John Kacur

Documentation

Installation

Get the latest sources from the git repository, do a git clone git://git.kernel.org/pub/scm/utils/rt-tests/rt-tests.git or fetch a released tarball from the archive, untar into a directory of your choice and run make in the source directory. If you want to cross compile, just run make CROSS_COMPILE= (for example make CROSS_COMPILE=arm-v4t-linux-gnueabi-). 　　You can run the resulting binary from there or install it.

lgs@f11#> git clone git://git.kernel.org/pub/scm/utils/rt-tests/rt-tests.git lgs@f11#> cd rt-testslgs@f11#> make alllgs@f11#> cp ./cyclictest /usr/bin/lgs@f11#> cyclictest --help

NOTE! libnuma is required to build cyclictest. Usually, it’s safe to have libnuma installed also in non-numa systems, but if you don’t want to install the numa libs (e.g. in embedded environment) then compile with make NUMA=0.

Run it

Make sure to be root or use sudo to run cyclictest. Without parameters cyclictest creates one thread with a 1ms interval timer. cyclictest -h provides help text for the various options

[lgs@f11 rt-tests]#[lgs@f11 rt-tests]#[lgs@f11 rt-tests]# ./cyclictest --helpcyclictest V 0.42Usage:cyclictest -a [NUM] --affinity run thread #N on processor #N, if possible with NUM pin all threads to the processor NUM-b USEC --breaktrace=USEC send break trace command when latency > USEC-B --preemptirqs both preempt and-c CLOCK --clock=CLOCK 0 = CLOCK_MONOTONIC (default) 1 = CLOCK_REALTIME-C-d DIST --distance=DIST distance of thread intervals in us default=500-E-f --ftrace function trace (when-i INTV --interval=INTV base interval of thread in us default=1000-I --irqsoff Irqsoff-l LOOPS --loops=LOOPS number of loops: default=0(endless)-m --mlockall lock current and-n --nanosleep use clock_nanosleep-N --nsecs print results in-o RED --oscope=RED oscilloscope mode, reduce verbose output by RED-O TOPT --traceopt=TOPT-p PRIO --prio=PRIO-P --preemptoff Preempt-q --quiet print only a summary on exit-r --relative use relative timer instead of absolute-s --system use sys_nanosleep and-T TRACE --tracer=TRACER configured tracers: unavailable (debugfs not mounted)-t --threads one thread per available processor-t [NUM] --threads=NUM number of threads: without NUM, threads = max_cpus without -t default = 1-v --verbose output values on stdout for format: n:c:v n=tasknum c=count v=value in us-D --duration=t specify a length for default is in seconds, but 'm', 'h', or 'd' maybe added to modify value to minutes, hours or days-h --histogram=US US is the max time to be be tracked in microseconds-w --wakeup task wakeup tracing (used with -b)-W

-b is a debugging option to control the latency tracer in the realtime preemption patch. It is useful to track down unexpected large latencies on a system. This option does only work with

CONFIG_PREEMPT_RT=yCONFIG_WAKEUP_TIMING=yCONFIG_LATENCY_TRACE=yCONFIG_CRITICAL_PREEMPT_TIMING=yCONFIG_CRITICAL_IRQSOFF_TIMING=y

kernel configuration options enabled. The USEC parameter to the -b option defines a maximum latency value, which is compared against the actual latencies of the test. Once the measured latency is higher than the given maximum, the kernel tracer and cyclictest is stopped. The trace can be read from /proc/latency_trace mybox# cat /proc/latency_trace >trace.log Please be aware that the tracer adds significant overhead to the kernel, so the latencies will be much higher than on a kernel with latency tracing disabled. -c CLOCK selects the clock, which is used

0 selects CLOCK_MONOTONIC, which is the monotonic increasing systemtime. This is the default selection1 selects CLOCK_REALTIME, which is the time of day time.

CLOCK_REALTIME can be set by settimeofday, while CLOCK_MONOTONIC can not be modified by the user. This option has no influence when the -s option is given. -d DIST set the distance of thread intervals in microseconds (default is 500us) When cylictest is called with the -t option and more than one thread is created, then this distance value is added to the interval of the threads. Interval(thread N) = Interval(thread N-1) + DIST -i INTV set the base interval of the thread(s) in microseconds (default is 1000us) This sets the interval of the first thread. See also -d. -l LOOPS set the number of loops (default = 0(endless)) This option is useful for automated tests with a given number of test cycles. cyclictest is stopped once the number of timer intervals has been reached. -n use clock_nanosleep instead of posix interval timers Setting this option runs the tests with clock_nanosleep instead of posix interval timers. -p PRIO set the priority of the first thread The given priority is set to the first test thread. Each further thread gets a lower priority: Priority(Thread N) = Priority(Thread N-1) -q run the tests quiet and print only a summary on exit Useful for automated tests, where only the summary output needs to be captured -r use relative timers instead of absolute The default behaviour of the tests is to use absolute timers. This option is there for completeness and should not be used for reproducible tests. -s use sys_nanosleep and sys_setitimer instead of posix timers Note, that -s can only be used with one thread because itimers are per process and not per thread. -s in combination with -n uses the nanosleep syscall and is not restricted to one thread -t NUM set the number of test threads (default is 1), -t without an argument makes the number of threads equal to the number of cpus Create NUM test threads. See -d, -i and -p for further information. -v output values on stdout for statistics This option is used to gather statistical information about the latency distribution. The output is sent to stdout. The output format is n:c:v where n=task number c=count v=latency value in us Use this option in combination with -l The OSADL Realtime LiveCD project provides a script to plot the latency distribution.

Expected Results

tglx’s reference machine

All tests have been run on a Pentium III 400MHz based PC. 　　The tables show comparisons of vanilla Linux 2.6.16, Linux-2.6.16-hrt5 and Linux-2.6.16-rt12. The tests for intervals less than the jiffy resolution have not been run on vanilla Linux 2.6.16. The test thread runs in all cases with SCHED_FIFO and priority 80. All numbers are in microseconds.

Test case: clock_nanosleep(TIME_ABSTIME), Interval 10000microseconds,. 10000 loops, no load.

Commandline: ​​cyclictest -t1 -p 80 -n -i 10000 -l 10000​​​ Kernel min max avg 2.6.16 24 4043 1989 2.6.16-hrt5 12 94 20 2.6.16-rt12 6 40 10

Test case: clock_nanosleep(TIME_ABSTIME), Interval 10000 microseconds,. 10000 loops, 100% load.

Commandline: ​​cyclictest -t1 -p 80 -n -i 10000 -l 10000​​​ Kernel min max avg 2.6.16 55 4280 2198 2.6.16-hrt5 11 458 55 2.6.16-rt12 6 67 29

Test case: POSIX interval timer, Interval 10000 micro seconds,. 10000loops, no load.

Commandline: ​​cyclictest -t1 -p 80 -i 10000 -l 10000​​​ Kernel min max avg 2.6.16 21 4073 2098 2.6.16-hrt5 22 120 35 2.6.16-rt12 20 60 31

Test case: POSIX interval timer, Interval 10000 micro seconds,. 10000loops, 100% load.

Commandline: ​​cyclictest -t1 -p 80 -i 10000 -l 10000​​​ Kernel min max avg 2.6.16 82 4271 2089 2.6.16-hrt5 31 458 53 2.6.16-rt12 21 70 35

Test case: clock_nanosleep(TIME_ABSTIME), Interval 500 microseconds,. 100000 loops, no load.

Commandline: ​​cyclictest -t1 -p 80 -i 500 -n -l 100000​​​ Kernel min max avg 2.6.16-hrt5 5 108 24 2.6.16-rt12 5 48 7

Test case: clock_nanosleep(TIME_ABSTIME), Interval 500 microseconds,. 100000 loops, 100% load.

Commandline: ​​cyclictest -t1 -p 80 -i 500 -n -l 100000​​​ Kernel min max avg 2.6.16-hrt5 9 684 56 2.6.16-rt12 10 60 22

Test case: POSIX interval timer, Interval 500 micro seconds,. 100000loops, no load.

Commandline: ​​cyclictest -t1 -p 80 -i 500 -l 100000​​​ Kernel min max avg 2.6.16-hrt5 8 119 22 2.6.16-rt12 12 78 16

Test case: POSIX interval timer, Interval 500 micro seconds,. 100000loops, 100% load.

Commandline: ​​cyclictest -t1 -p 80 -i 500 -l 100000​​​ Kernel min max avg 2.6.16-hrt5 16 489 58 2.6.16-rt12 12 95 29

FAQ

ps shows the wrong scheduling class SCHED_OTHER

Each cyclictest-task consist of one or more threads. ps -ce shows only the main-process not the threads of the main-process. ps -eLc | grep cyclic shows the main-process an the containing threads with the correct scheduler class SCHED_FIFO.

#>./cyclictest -t5 -p 80 -n -i 10000#> ps -cLe | grep cyclic 4764 4764 TS 19 pts/1 00:00:01 cyclictest 4764 4765 FF 120 pts/1 00:00:00 cyclictest 4764 4766 FF 119 pts/1 00:00:00 cyclictest 4764 4767 FF 118 pts/1 00:00:00 cyclictest 4764 4768 FF 117 pts/1 00:00:00 cyclictest 4764 4769 FF 116 pts/1 00:00:00

chrt shows the wrong scheduling class SCHED_OTHER

Don’t use the PID of the main-process, but the pid of one of the threads from the main-process. The threads are shown with ps -cLe | grep cyclic.

#> chrt -p 4766pid 4766's current scheduling policy: SCHED_FIFOpid 4766's current scheduling priority: 79

taskset for CPU affinity

taskset command is Written by Robert M. Love. SMP operating systems have choices when it comes to scheduling processes: a new or newly rescheduled process can run on any available cpu. However, while it shouldn’t matter where a new process runs, an existing process should go back to the same cpu it was running on simply because the cpu may still be caching data that belongs to that process. This is particularly apt to be true if the process is a thread: the other threads in the same program are very likely to have cpu cache of interest to their brethren (though obviously this also diminishes the performance gain that might be seen from multithreading) . For these reasons, scheduling algorithms pay attention to cpu affinity and try to keep it constant. 　　It is possible to force a process to run only on a certain cpu. There are Linux system calls (sched_setaffinity and sched_getaffinity) and a command line “taskset”.

lgs@f11#> taskset -c 3 toplgs@f11#> taskset -p [pid]

Compile failure because numa.h can’t be found

makecc -D VERSION_STRING=0.85 -c src/cyclictest/cyclictest.c -Wall -Wno-nonnull -O2 -DNUMA -D_GNU_SOURCE -Isrc/includeIn file included from src/cyclictest/cyclictest.c:37:0:src/cyclictest/rt_numa.h:23:18: fatal error: numa.h: No such file or directorycompilation terminated.make: *** [cyclictest.o] Error 1

Simply install your distribution’s numa development package. On Fedora this is numactl-devel, so

su -c 'yum install numactl-devel'

This is only required for building. This will not affect the way the test runs on non-numa machines

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