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MMTests: Benchmarking framework primarily aimed at Linux kernel testing

Overview

MMTests is a configurable test suite that runs performance tests against arbitrary workloads. This is not the only test framework but care is taken to make sure the test configurations are accurate, representative and reproducible. Reporting and analysis is common across all benchmarks. Support exists for gathering additional telemetry while tests are running and hooks exist for more detailed tracing using ftrace or perf.

Quick Introduction

The top-level directory has a single driver script called run-mmtests.sh which reads a config file that describes how the benchmarks should be configured and executed. In some cases, the same benchmarking tool may be used with different configurations that stresses the scenario.

A test run can have any name. A common use case is simply to compare kernel versions but it can be anything —different compiler, different userspace package, different benchmark configuration etc.

Monitors can be optionally configured, but care should be taken as there is a possibility that they introduce overhead of their own. Hence, for some performance sensitive tests it is preferable to have no monitoring.

Many of the tests download external benchmarks. An attempt will be made to download from a mirror if it exists. To get an idea where the mirror should be located, grep for MIRROR_LOCATION= in shellpacks/.

A basic invocation of the suite is

$ ./bin/autogen-configs
$ ./run-mmtests.sh --no-monitor --config configs/config-pagealloc-performance 5.8-vanilla
$ ./run-mmtests.sh --no-monitor --config configs/config-pagealloc-performance 5.9-vanilla
$ cd work/log
$ ../../compare-kernels.sh
$ mkdir /tmp/html/
$ ../../compare-kernels.sh --format html --output-dir /tmp/html > /tmp/html/index.html

The first step is optional. Some configurations are auto-generated from a template, particularly the filesystem-specific ones.

Note that List::BinarySearch and maybe even Math::Gradient may need to be installed from CPAN for the reporting to work. Similarly, R should be installed if attempting to highlight whether performance differences are statistically relevant.

A tutorial with some more details and the full output of each step is available here:

Running Benchmarks with MMTests

Configuration

All available configurations are stored in configs/.

For example config-pagealloc-performance can be used to run tests that may be able to identify performance regressions or gains in the page allocator. Similarly there are network, disk and scheduler configs.

The config file can take many options, in the form of export-ed variables. there is a functional sample config file available in config.

Some options are universal, others are specific to the test. Some of the universal ones are:

  • MMTESTS: A list of what tests will be run.
  • AUTO_PACKAGE_INSTALL: Whether packages necessary for building or running benchmarks should be automatically installed, without asking any confirmation (takes a yes or a no). Creating a file called .mmtests-auto-package-install and putting it in / would be equivalent of having this set to yes.
  • MMTESTS_NUMA_POLICY: Whether numad or numactl should be used for deciding (typically, for restricting) on what CPUs and/or NUMA nodes the benchmark will run. It accepts several values. none, numad or interleave, are the simplest, but the following ones can also be used:
    • fullbind_single_instance_node
    • fullbind_single_instance_cpu
    • membind_single_instance_node
    • cpubind_single_instance_node
    • membind_single_instance_node
    • membind_single_instance_node
    • cpubind_largest_nonnode0_memory, in which case, MMTESTS_NODE_ID should also be defined
    • cpubind_node_nrcpus, in which case MMTESTS_NUMA_NODE_NRCPUS should also be defined. If none is used or the option is not present, nothing is done in terms of NUMA pinning of the benchmarks.
  • MMTESTS_TUNED_PROFILE: Whether or not the tuned tool should be used and, if yes, with which profile. In fact, the option takes the name of the desired profile (which should be present in the system). If this is defined tuned is started and stopped around the execution of the benchmarks.
  • SWAP_CONFIGURATION, SWAP_PARTITIONS, SWAP_SWAPFILE_SIZEMB: It's possible to use a different swap configuration than what is provided by default.
  • TESTDISK_RAID_DEVICES, TESTDISK_RAID_MD_DEVICE, TESTDISK_RAID_OFFSET, TESTDISK_RAID_SIZE, TESTDISK_RAID_TYPE: If the target machine has partitions suitable for configuring RAID, they can be specified here. This RAID partition is then used for all the tests.
  • TESTDISK_PARTITION: Use this partition for all tests.
  • TESTDISK_FILESYSTEM, TESTDISK_MKFS_PARAM, TESTDISK_MOUNT_ARGS: The filesystem, mkfs parameters and mount arguments for the test partitions.
  • TESTDISK_DIR: A directory passed to the test. If not set, defaults to SHELLPACK_TEMP. The directory is supposed to contain a precreated environment (eg. a specifically created filesystem mounted with desired mount options).
  • STORAGE_CACHE_TYPE, STORAGE_CACHING_DEVICE, STORAGE_BACKING_DEVICE: It's also possible to use storage caching. STORAGE_CACHE_TYPE is either "dm-cache" or "bcache". The devices specified with STORAGE_CACHING_DEVICE and STORAGE_BACKING_DEVICE are used to create the cache device which then is used for all the tests.

Platform Specific Configuration

It is possible to retrieve information about the characteristics of the system where the benchmarks will be running, and use them inside a config file.

For instance:

  • MEMTOTAL_BYTES: Tells how much memory there is in the system.
  • NUMCPUS: Tells how many CPUs are present in the system.

It is possible to add the following to the config file:

. $SHELLPACK_INCLUDE/include-sizes.sh
get_numa_details

This will give access to more information about the system topology, such as:

  • NUMLLCS: Number of Last Level Caches present in the system.
  • NUMNODES: Number of NUMA nodes.

Benchmark configurations can then be refined, by taking advantage of the knowledge of the platform characteristics.

For an example check config-workload-stream-omp-llcs, where this is done: STREAM_THREADS=$NUMLLCS. Or config-scheduler-schbench, which has: SCHBENCH_THREADS=$(((NUMCPUS/NUMNODES)-1))

Running Benchmarks

The entry point to running benchmarks is run-mmtests.sh. If run with -h or --help the available options are shown:

 run-mmtests [-mnpb] [-c config-file] test-name

  Options:
  -m|--run-monitors         Run with monitors enabled as specified by the configuration
  -n|--no-monitor           Only execute the benchmark, do not monitor it
  -p|--performance          Set the performance cpufreq governor before starting
  -c|--config               Configuration file to read (default: ./config)
  -b|--build-only           Only build the benchmark, do not execute it

If no config file is specified, the one in ./config is used.

After a run, the benchmark results as well as any data that can be useful for a report will be available in the work/log directory. (more specifically, in work/log/TEST_RUN/iter-0, for a run called TEST_RUN).

Note that often a configuration will run more than just one single benchmark (this depends on the value of the MMTESTS option in the config itself), resulting in some subdirectories being present in the results directory.

Running MMTests as root

Configuring the system for running a benchmark may include doing some changes to the system itself that can only be done with root provileges.

For instance, the config-workload-thpchallenge-fio-defrag config does:

echo always > /sys/kernel/mm/transparent_hugepage/defrag

If starting run-mmtests.sh as a "regular user" doing something like that will fail. benchmarks should still complete (most likely with some warnings) but results will likely not be the ones expected.

In fact, MMTests is intended to be run as root. For most of the changes that it applies to the system, the framework is careful to (try to) undo them. It is however fair to say that MMTests is best used on machines that can be redeployed and reset to a clean known state both before and after running a benchmark.

Monitoring

A full list of available monitors is in monitors/.

The following options, to be defined in the config file, can be used to control monitoring:

  • RUN_MONITOR: yes or no switch for deciding whether monitoring should happen or not, during the execution of the benchmarks. If set to no, even if monitors are defined, they will be ignored (but see MONITOR_ALWAYS below). It can be overridden by the --run-monitors and --no-monitor command line parameters. I.e., --run-monitors means we will always run monitors, even if we have RUN_MONITOR=no in the config file (and vice versa, for --no-monitor and RUN_MONITOR=yes).
  • MONITORS_ALWAYS: Basically, another override. In fact, monitors defined here will be started even if we have RUN_MONITOR=no and/or --no-monitor.
  • MONITORS_GZIP: A list of monitors to be used during the benchmarks. Their output will be saved in compressed (with gzip) log files.
  • MONITORS_WITH_LATENCY: A list of monitors to be used during the benchmarks with their output augmented with some additional timestamping.
  • MONITOR_UPDATE_FREQUENCY: How frequently, in seconds, the various defined monitors should produce and log a sample.
  • MONITOR_FTRACE_OPTIONS, MONITOR_FTRACE_EVENTS: respectively, options to set and tracing events to enable for ftrace, if the "ftrace" monitor is enabled.
  • MONITOR_PERF_EVENTS: list of perf events to stat or record, when any of the "perf-foo" monitor is enabled (see below).

The files in monitors/ all follow the same naming scheme, which is watch-foo.[sh|pl]. For instance, we have monitors/watch-mpstat.sh, monitors/watch-proc-interrupts.sh monitors/watch-proc-vmstat.sh. For monitoring the output of mpstat and the content of /proc/interrupts and /proc/vmstat during the execution of a benchmark, include this option in to the config file: MONITORS_GZIP="proc-vmstat mpstat proc-interrupts"

Similarly, to monitor the output of vmstat and iostat, and also add some timestamps to the output, define this option: MONITORS_WITH_LATENCY="vmstat iostat".

In order to record the output of, for instance, the sched_migrate_task tracepoint, make sure to have ftrace in the list of monitors defined in MONITORS_GZIP and then add MONITOR_FTRACE_EVENTS="sched/sched_migrate_task". (See also configs/config-monitor-vm-stalls for a more advanced example.)

For using perf "as a monitor", a list of events should be defined, e.g. MONITOR_PERF_EVENTS=cpu-migrations,context-switches or MONITOR_PERF_EVENTS=node-load-misses,node-store-misses. Also, the monitor should be defined either adding perf-time-stat to the list of MONITORS_GZIP, or adding perf-event-stat to the MONITORS_TRACER option.

Reporting

Reporting with compare-kernel.sh

For reporting, there is a basic compare-kernels.sh script.

Despite the name, it can compare an arbitrary number of benchmarking runs. The name has historical reasons, from the time when the only use case was comparing kernel versions, but nowadays anything can be compared --machines, userspace packages, benchmark versions, tuning parameters etc.

It is optionally possible to specify a different baseline and comparison points, while by default the results are organised by the time the test was executed.

NAME
    compare-kernels.sh - Compare results between benchmarking runs

SYNOPSIS
    compare-kernels.sh [options]

     Options:
      --baseline <testname>         Baseline test name, default is time ordered
      --compare  "<test> <test>"    Comparison test names, space separated
      --exclude  "<test> <test>"    Exclude test names
      --auto-detect                 Attempt to automatically highlight significant differences
      --sort-version                Assume kernel versions for test names and attempt to sort
      --format html                 Generate a HTML format of the report
      --output-dir                  Output directory for HTML report

It must be run from within an MMTests results directory. So, even if the benchmarks have been run on a different machine, it is enought to capture work/log and run compare-kernels.sh from there.

In the table(s) produced, it is usually the most interesting to look at the average values, computed over the individual results of multiple repetitions of the benchmarks. Note that some benchmarks use the harmonic mean (Hmean) and some use the arithmetic mean (Amean), depending of the nature of the results.

compare-kernel.sh can generate an HTML report, with both tables and graphs. For doing that, both the format and the output directory needs to be specified. The HTML page will then come directly out of the standard output of the tool. Therefore, invoking it like this is recommended:

$ cd work/log
$ mkdir /tmp/report
$ ../../compare-kernels.sh --format html --output-dir /tmp/report > /tmp/report/index.html

An example of the HTML reporting is available here. This comes from two simple runs of the default config (i.e., of the STREAM benchmark) when the system was idle (TEST_RUN) and busy with something else (TEST_RUN_BUSY).

Reporting with compare-mmtestsl.pl

It is possible to obtain a report using a different tool. It is the script that compare-kernels.sh calls internally and it is located at bin/compare-mmtests.pl.

The output is the same table(s) produced by compare-kernels.sh.

A possible invocation could look like this:

./bin/compare-mmtests.pl --directory work/log --benchmark stream --names TEST_RUN,TEST_RUN_BUSY
                           TEST_RUN          TEST_RUN_BUSY
MB/sec copy     19059.86 (   0.00%)    15234.88 ( -20.07%)
MB/sec scale    14078.10 (   0.00%)    11258.38 ( -20.03%)
MB/sec add      14740.32 (   0.00%)    11749.84 ( -20.29%)
MB/sec triad    14504.22 (   0.00%)    11317.26 ( -21.97%)

If the benchmark does multiple operations —like STREAM above that checks the memory throughput of four different operations— there will be one result for each. In these cases, compare-mmtests.pl can be used to produce an overall comparison between the benchmarks.

This is done by taking the geometric mean (Gmean) of the results. The geometric mean is chosen because it has the nice property that the mean of ratios is equal to the ratios of the means, so we do not get different results depending on the order of the operations.

Looking at the Gmean offers a concise and hence rather useful overview of the overall performance, especially when complex benchmarks are used.

For instance:

./bin/compare-mmtests.pl --directory work/log/ --benchmark stream --names TEST_RUN,TEST_RUN_BUSY --print-ratio
                          TEST_RUN          TEST_RUN_BUSY
Ratio copy         1.00 (0.00%) (NaNs)        0.80 (-20.07%) (NaNs)
Ratio scale        1.00 (0.00%) (NaNs)        0.80 (-20.03%) (NaNs)
Ratio add          1.00 (0.00%) (NaNs)        0.80 (-20.29%) (NaNs)
Ratio triad        1.00 (0.00%) (NaNs)        0.78 (-21.97%) (NaNs)
Gmean Higher        1.00                         0.79

Of course, the Gmean for the benchmark chosen as the baseline will always be 1.00. Additionally, the Higher or Lower label tells us whether it is the higher or lower values that represent better performance.

In the example above, TEST_RUN_BUSY reaches only the 79% of TEST_RUN performance, which means that it is 21% slower.

Further info about reporting:

MMTests Internal Structure & Development

Benchmarks & Shellpacks

The install and test scripts are automatically generated from "shellpacks". A shellpack is a pair of benchmark and install scripts that are stored in shellpacks/.

Actual shellpacks are automatically generated from template files stored in shellpack_src/src/. Some have a build suffix indicating that it is only building a supporting tool like a library a benchmark requires. Do not modify the generated test-scripts in shellpacks/ directory as they will simply be overwritten.

For instance, /shellpacks/shellpack-bench-pgbench —which will be automatically generated from shellpack_src/src/pgbench/pgbench-bench— contains all the individual test steps.

Each test is driven by bin/run-single-test.sh script which reads the relevant drivers/driver-<testname>.sh script (e.g., drivers/driver-pgbench.sh).

Downloading Benchmarks & Mirrors

MMTests needs to download the various benchmarks from their official location, i.e., from the Internet. That might be problematic because it can (should!) be considered not trusted, or even just because the official repository may have been updated to a newer version which maybe is not yet compatible with the current release of MMTests. And if this happens, the run will likely fail.

Other potential problems are that the download may fail due to temporary networking issues, that it consumes bandwidth and that it adds delays and makes testing longer.

It is therefore possible to create a local mirror. The location of such mirror can be configured in WEBROOT in shellpacks/common-config.sh.

For example, kernbench tries to download $WEBROOT/kernbench/linux-3.0.tar.gz. If this is not available, it is downloaded from the internet. This can add delays in testing and consumes bandwidth so is worth configuring.

Contributing and Bug Reporting

Patches should be sent to Mel Gorman <[email protected]>. While the project is hosted on github, notifications get lost so pull requests there may be missed for quite a long time.

References

(Pseudo-)Random links to when MMTests got mentioned around in the Internet:

  • MMTests being used to benchmark patches to the task wake-up path inside the Linux scheduler, on LKML here and here.
  • MMTests used to reproduce a bug in the accounting code inside the Linux scheduler, on LKML.
  • MMTests used to benchmark some early version of the Core Scheduling patches, highlighting their impact on both baremetal and virtualization workloads, on LKML (check the replies for seeing all the benchmark results).
  • Additionally to the above examples, a lot more reports of MMTests being used for Linux kernel development can be found just by searching for 'MMTests' in an LKML archive.
  • Giovanni Gherdovich explaining running MMTests and reading the reporting on LKML.

Talks and presentation about or related to MMTests:

Some historic references:

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