CoreSight - Perf


Carsten Haitzler <>


June 29th, 2022

Perf is able to locally access CoreSight trace data and store it to the output perf data files. This data can then be later decoded to give the instructions that were traced for debugging or profiling purposes. You can log such data with a perf record command like:

perf record -e cs_etm//u testbinary

This would run some test binary (testbinary) until it exits and record a trace file. That file would have AUX sections if CoreSight is working correctly. You can dump the content of this file as readable text with a command like:

perf report --stdio --dump -i

You should find some sections of this file have AUX data blocks like:

0x1e78 [0x30]: PERF_RECORD_AUXTRACE size: 0x11dd0  offset: 0  ref: 0x1b614fc1061b0ad1  idx: 0  tid: 531230  cpu: -1

. ... CoreSight ETM Trace data: size 73168 bytes
        Idx:0; ID:10;   I_ASYNC : Alignment Synchronisation.
          Idx:12; ID:10;  I_TRACE_INFO : Trace Info.; INFO=0x0 { CC.0 }
          Idx:17; ID:10;  I_ADDR_L_64IS0 : Address, Long, 64 bit, IS0.; Addr=0x0000000000000000;
          Idx:26; ID:10;  I_TRACE_ON : Trace On.
          Idx:27; ID:10;  I_ADDR_CTXT_L_64IS0 : Address & Context, Long, 64 bit, IS0.; Addr=0x0000FFFFB6069140; Ctxt: AArch64,EL0, NS;
          Idx:38; ID:10;  I_ATOM_F6 : Atom format 6.; EEEEEEEEEEEEEEEEEEEEEEEE
          Idx:39; ID:10;  I_ATOM_F6 : Atom format 6.; EEEEEEEEEEEEEEEEEEEEEEEE
          Idx:40; ID:10;  I_ATOM_F6 : Atom format 6.; EEEEEEEEEEEEEEEEEEEEEEEE
          Idx:41; ID:10;  I_ATOM_F6 : Atom format 6.; EEEEEEEEEEEN

If you see these above, then your system is tracing CoreSight data correctly.

To compile perf with CoreSight support in the tools/perf directory do:


This requires OpenCSD to build. You may install distribution packages for the support such as libopencsd and libopencsd-dev or download it and build yourself. Upstream OpenCSD is located at:

For complete information on building perf with CoreSight support and more extensive usage look at:

Kernel CoreSight Support

You will also want CoreSight support enabled in your kernel config. Ensure it is enabled with:


There are various other CoreSight options you probably also want enabled like:


Please refer to the kernel configuration help for more information.

Perf test - Verify kernel and userspace perf CoreSight work

When you run perf test, it will do a lot of self tests. Some of those tests will cover CoreSight (only if enabled and on ARM64). You generally would run perf test from the tools/perf directory in the kernel tree. Some tests will check some internal perf support like:

Check Arm CoreSight trace data recording and synthesized samples Check Arm SPE trace data recording and synthesized samples

Some others will actually use perf record and some test binaries that are in tests/shell/coresight and will collect traces to ensure a minimum level of functionality is met. The scripts that launch these tests are in the same directory. These will all look like:

CoreSight / ASM Pure Loop CoreSight / Memcpy 16k 10 Threads CoreSight / Thread Loop 10 Threads - Check TID etc.

These perf record tests will not run if the tool binaries do not exist in tests/shell/coresight/*/ and will be skipped. If you do not have CoreSight support in hardware then either do not build perf with CoreSight support or remove these binaries in order to not have these tests fail and have them skip instead.

These tests will log historical results in the current working directory (e.g. tools/perf) and will be named stats-*.csv like:

stats-asm_pure_loop-out.csv stats-memcpy_thread-16k_10.csv ...

These statistic files log some aspects of the AUX data sections in the perf data output counting some numbers of certain encodings (a good way to know that it’s working in a very simple way). One problem with CoreSight is that given a large enough amount of data needing to be logged, some of it can be lost due to the processor not waking up in time to read out all the data from buffers etc.. You will notice that the amount of data collected can vary a lot per run of perf test. If you wish to see how this changes over time, simply run perf test multiple times and all these csv files will have more and more data appended to it that you can later examine, graph and otherwise use to figure out if things have become worse or better.

This means sometimes these tests fail as they don’t capture all the data needed. This is about tracking quality and amount of data produced over time and to see when changes to the Linux kernel improve quality of traces.

Be aware that some of these tests take quite a while to run, specifically in processing the perf data file and dumping contents to then examine what is inside.

You can change where these csv logs are stored by setting the PERF_TEST_CORESIGHT_STATDIR environment variable before running perf test like:

perf test

They will also store resulting perf output data in the current directory for later inspection like:

You can alter where the perf data files are stored by setting the PERF_TEST_CORESIGHT_DATADIR environment variable such as:

perf test

You may wish to set these above environment variables if you wish to keep the output of tests outside of the current working directory for longer term storage and examination.