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Tomas Glozar
fafb66e590
A bug was reported when rtla-timerlat-top tool performs on-threshold
actions, even though no threshold was hit. This is reproduced even if no
threshold is set at all:
$ rtla timerlat top -q -c 0 --on-threshold shell,command='echo BAD'
BAD
Timer Latency
...
The bug is due to incorrect logic in timerlat_top_bpf_main_loop().
The loop uses timerlat_bpf_wait(), the return values of which are:
- > 0 (number of ringbuffer entries): at least 1 CPU hit threshold
- = 0: time out
- < 0: wait was interrupted by a signal
Commit 3138df6f0c ("rtla/timerlat: Exit top main loop on any non-zero
wait_retval") changed the condition for "threshold hit" from
"wait_reval == 1" (exactly 1 CPU hit threshold) to "wait_retval != 0",
to fix a race where multiple CPUs hit the threshold at the same time.
That also made it incorrectly include a signal (< 0), coming from either
duration expired (SIGALRM) or user interrupt (SIGINT).
Check for wait_retval greater than zero in the if condition to cover all
return values correctly.
Fixes: 3138df6f0c ("rtla/timerlat: Exit top main loop on any non-zero wait_retval")
Reported-by: Attila Fazekas <afazekas@redhat.com>
Reviewed-by: Wander Lairson Costa <wander@redhat.com>
Link: https://lore.kernel.org/r/20260713141047.687877-1-tglozar@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>
RTLA: Real-Time Linux Analysis tools The rtla meta-tool includes a set of commands that aims to analyze the real-time properties of Linux. Instead of testing Linux as a black box, rtla leverages kernel tracing capabilities to provide precise information about the properties and root causes of unexpected results. Installing RTLA RTLA depends on the following libraries and tools: - libtracefs - libtraceevent - libcpupower (optional, for --deepest-idle-state) - libcheck (optional, for unit tests) For BPF sample collection support, the following extra dependencies are required: - libbpf 1.0.0 or later - bpftool with skeleton support - clang with BPF CO-RE support It also depends on python3-docutils to compile man pages. For development, we suggest the following steps for compiling rtla: $ git clone git://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git $ cd libtraceevent/ $ make $ sudo make install $ cd .. $ git clone git://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git $ cd libtracefs/ $ make $ sudo make install $ cd .. $ cd $libcpupower_src $ make $ sudo make install $ cd $rtla_src $ make $ sudo make install Running tests RTLA has two test suites: a runtime test suite and a unit test suite. The runtime test suite is available as "make check" (root required) and has the following dependencies, in addition to RTLA build dependencies: - Perl - Test::Harness (libtest-harness-perl on Debian/Ubuntu, perl-Test-Harness on Fedora/RHEL) - bash - coreutils - ldd - util-linux - procps(-ng) - bpftool (if rtla is built against libbpf) as well as the following required system configuration: - CONFIG_OSNOISE_TRACER=y - CONFIG_TIMERLAT_TRACER=y - tracefs mounted and readable at /sys/kernel/tracing The unit test suite is available as "make unit-tests" and has the following dependencies: - libcheck Unlike the runtime test suite, root is not required to run unit tests, nor is a tracefs/osnoise/timerlat-capable kernel required. For further information, please refer to the rtla man page.