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likwid-java-api

A Java API for the performance monitoring and benchmarking suite called likwid (https://github.com/rrze-likwid/likwid)

This API allows you to put tagged markers into your code so that only those parts of your code will be measured by likwid-perfctr.

Requirements

Note: If you are running Linux in a virtual machine, make sure it is VMWare. To my knowledge, VirtualBox doesn't support performance counters so this stuff won't work.

Installation

In order to use this API, you need to:

git clone https://github.com/jlewandowski/likwid-java-api.git likwid-java-api

mvn clean install

likwid-perfctr -C 0 -g TLB_DATA -m java -DLIKWID_PERFMON -cp target/likwid-java-api-1.0-SNAPSHOT.jar org.jl.perftools.likwid.examples.Example1

Enable/Disable

Likwid markers works there is LIKWID_PERFMON system property defined. You also need to run likwid-perfctr with -m parameter to enable measurements for marked regions.

If LIKWID_PERFMON is not defined, an empty API implementation will be returned to the user. Therefore, Java should inline all the empty method and it should have no impact on the performance.

Example

The full example code can be found in Java sources. This is the only important part:

// Initialize marker API and get its instance. If marker API is not available or disabled, it will return
// a dummy implementation which will be inlined by Java VM and no performance impact will be introduced.
ILikwidMarker marker = LikwidMarkerAPIProvider.getInstance();

// Need to init marker API ahead of registering any marker
marker.init();
try {
    // warm-up for 1st test
    for (int i = 0; i < warmUpItrs; i++) test1(amount);

    // Likwid will be aware if the code region is repeated and it will calculate average ratios
    for (int i = 0; i < iterations; i++) {
        // Open a tagged code region for measurements
        marker.start("test1");
        test1(amount);
        // Closed a tagged code region for measurements
        marker.stop("test1");
    }

    // warm-up for 2nd test
    for (int i = 0; i < warmUpItrs; i++) test2(amount);
    for (int i = 0; i < iterations; i++) {
        // Open another tagged code region for measurements
        marker.start("test2");
        test2(amount);
        // Closed a tagged code region for measurements
        marker.stop("test2");
    }

} finally {
    // Remember to close the marker API
    marker.close();
}

The interesting methods which we want to test performance of are test1 and test2. We would like to compare them, so we enclose their invocations by marking start and stop of tagged region. The code inside a single region can be invoked multiple times - in this case, likwid will sum the number of events and average the calculated ratios.

An output of this example could be:

# likwid-perfctr -C 0 -g TLB_DATA -m java -DLIKWID_PERFMON -cp target/likwid-java-api-1.0-SNAPSHOT.jar org.jl.perftools.likwid.examples.Example1
--------------------------------------------------------------------------------
CPU name:	Intel(R) Core(TM) i7-4850HQ CPU @ 2.30GHz
CPU type:	Intel Core Haswell processor
CPU clock:	2.29 GHz
--------------------------------------------------------------------------------
Likwid markers are enabled.
LikwidMarkerResults{events=[], time=0.3667285972945661, count=5}
LikwidMarkerResults{events=[], time=6.979190770504919, count=5}
Which just means that test2 was on average 19.030942 faster than test1
0
--------------------------------------------------------------------------------
================================================================================
Group 1 TLB_DATA: Region test1
================================================================================
+-------------------+----------+
|    Region Info    |  Core 0  |
+-------------------+----------+
| RDTSC Runtime [s] | 0.366729 |
|     call count    |     5    |
+-------------------+----------+

This above fragment says that the code inside test1 region was executed 5 times, which took 0.367 s in total.


+---------------------------------+---------+--------------+
|              Event              | Counter |    Core 0    |
+---------------------------------+---------+--------------+
|        INSTR_RETIRED_ANY        |  FIXC0  | 3.875063e+09 |
|      CPU_CLK_UNHALTED_CORE      |  FIXC1  | 1.260274e+09 |
|       CPU_CLK_UNHALTED_REF      |  FIXC2  | 8.292720e+08 |
|  DTLB_LOAD_MISSES_CAUSES_A_WALK |   PMC0  | 4.925000e+03 |
| DTLB_STORE_MISSES_CAUSES_A_WALK |   PMC1  | 1.290000e+03 |
|  DTLB_LOAD_MISSES_WALK_DURATION |   PMC2  | 4.292070e+05 |
| DTLB_STORE_MISSES_WALK_DURATION |   PMC3  | 1.686980e+05 |
+---------------------------------+---------+--------------+

+-----------------------------------+--------------+
|               Metric              |    Core 0    |
+-----------------------------------+--------------+
|        Runtime (RDTSC) [s]        |   0.3667286  |
|        Runtime unhalted [s]       | 5.491927e-01 |
|            Clock [MHz]            | 3.487451e+03 |
|                CPI                | 3.252267e-01 |
|        L1 DTLB load misses        |     4925     |
|       L1 DTLB load miss rate      | 1.270947e-06 |
|  L1 DTLB load miss duration [Cyc] | 8.714863e+01 |
|        L1 DTLB store misses       |     1290     |
|      L1 DTLB store miss rate      | 3.328978e-07 |
| L1 DTLB store miss duration [Cyc] | 1.307736e+02 |
+-----------------------------------+--------------+

The above statistics says what happened in region test1 - for example, there were 4925 L1 DTLB load misses during all of the repetitions which gives 1.270947e-06 average ratio.

The region marked with test2 tag gives the following results:


================================================================================
Group 1 TLB_DATA: Region test2
================================================================================
+-------------------+----------+
|    Region Info    |  Core 0  |
+-------------------+----------+
| RDTSC Runtime [s] | 6.979191 |
|     call count    |     5    |
+-------------------+----------+

+---------------------------------+---------+--------------+
|              Event              | Counter |    Core 0    |
+---------------------------------+---------+--------------+
|        INSTR_RETIRED_ANY        |  FIXC0  | 3.875258e+09 |
|      CPU_CLK_UNHALTED_CORE      |  FIXC1  | 2.377920e+10 |
|       CPU_CLK_UNHALTED_REF      |  FIXC2  | 1.576489e+10 |
|  DTLB_LOAD_MISSES_CAUSES_A_WALK |   PMC0  | 1.002010e+09 |
| DTLB_STORE_MISSES_CAUSES_A_WALK |   PMC1  | 1.792100e+04 |
|  DTLB_LOAD_MISSES_WALK_DURATION |   PMC2  | 1.870362e+10 |
| DTLB_STORE_MISSES_WALK_DURATION |   PMC3  | 1.450194e+06 |
+---------------------------------+---------+--------------+

+-----------------------------------+--------------+
|               Metric              |    Core 0    |
+-----------------------------------+--------------+
|        Runtime (RDTSC) [s]        |   6.979191   |
|        Runtime unhalted [s]       | 1.036232e+01 |
|            Clock [MHz]            | 3.461358e+03 |
|                CPI                | 6.136159e+00 |
|        L1 DTLB load misses        |  1002010000  |
|       L1 DTLB load miss rate      | 2.585660e-01 |
|  L1 DTLB load miss duration [Cyc] | 1.866610e+01 |
|        L1 DTLB store misses       |     17921    |
|      L1 DTLB store miss rate      | 4.624466e-06 |
| L1 DTLB store miss duration [Cyc] | 8.092149e+01 |
+-----------------------------------+--------------+