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Add new option --bpf-action into common_timerlat_options.txt, including the format in which it takes the BPF program, and a reference to an example. Link: https://lore.kernel.org/r/20251126144205.331954-8-tglozar@redhat.com Signed-off-by: Tomas Glozar <tglozar@redhat.com>
85 lines
3.6 KiB
Text
85 lines
3.6 KiB
Text
.. |threshold| replace:: **-a/--auto**, **-i/--irq**, or **-T/--thread**
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.. |thresharg| replace:: -T
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.. |tracer| replace:: timerlat
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.. |actionsperf| replace::
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For time-sensitive actions, it is recommended to run **rtla timerlat** with BPF
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support and RT priority. Note that due to implementational limitations, actions
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might be delayed up to one second after tracing is stopped if BPF mode is not
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available or disabled.
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**-a**, **--auto** *us*
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Set the automatic trace mode. This mode sets some commonly used options
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while debugging the system. It is equivalent to use **-T** *us* **-s** *us*
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**-t**. By default, *timerlat* tracer uses FIFO:95 for *timerlat* threads,
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thus equivalent to **-P** *f:95*.
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**-p**, **--period** *us*
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Set the *timerlat* tracer period in microseconds.
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**-i**, **--irq** *us*
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Stop trace if the *IRQ* latency is higher than the argument in us.
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**-T**, **--thread** *us*
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Stop trace if the *Thread* latency is higher than the argument in us.
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**-s**, **--stack** *us*
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Save the stack trace at the *IRQ* if a *Thread* latency is higher than the
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argument in us.
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**-t**, **--trace** \[*file*]
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Save the stopped trace to [*file|timerlat_trace.txt*].
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**--dma-latency** *us*
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Set the /dev/cpu_dma_latency to *us*, aiming to bound exit from idle latencies.
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*cyclictest* sets this value to *0* by default, use **--dma-latency** *0* to have
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similar results.
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**--deepest-idle-state** *n*
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Disable idle states higher than *n* for cpus that are running timerlat threads to
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reduce exit from idle latencies. If *n* is -1, all idle states are disabled.
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On exit from timerlat, the idle state setting is restored to its original state
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before running timerlat.
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Requires rtla to be built with libcpupower.
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**-k**, **--kernel-threads**
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Use timerlat kernel-space threads, in contrast of **-u**.
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**-u**, **--user-threads**
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Set timerlat to run without a workload, and then dispatches user-space workloads
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to wait on the timerlat_fd. Once the workload is awakened, it goes to sleep again
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adding so the measurement for the kernel-to-user and user-to-kernel to the tracer
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output. **--user-threads** will be used unless the user specify **-k**.
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**-U**, **--user-load**
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Set timerlat to run without workload, waiting for the user to dispatch a per-cpu
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task that waits for a new period on the tracing/osnoise/per_cpu/cpu$ID/timerlat_fd.
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See linux/tools/rtla/example/timerlat_load.py for an example of user-load code.
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**--bpf-action** *bpf-program*
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Loads a BPF program from an ELF file and executes it when a latency threshold is exceeded.
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The BPF program must be a valid ELF file loadable with libbpf. The program must contain
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a function named ``action_handler``, stored in an ELF section with the ``tp_`` prefix.
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The prefix is used by libbpf to set BPF program type to BPF_PROG_TYPE_TRACEPOINT.
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The program receives a ``struct trace_event_raw_timerlat_sample`` parameter
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containing timerlat sample data.
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An example is provided in ``tools/tracing/rtla/example/timerlat_bpf_action.c``.
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This example demonstrates how to create a BPF program that prints latency information using
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bpf_trace_printk() when a threshold is exceeded.
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**Note**: BPF actions require BPF support to be available. If BPF is not available
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or disabled, the tool falls back to tracefs mode and BPF actions are not supported.
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