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kernel: add HWLAT_TRACER kernel config option

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This adds the HWLAT_TRACER kernel configuration option. The hwlat tracer
allows to detect hardware latencies.

Signed-off-by: Thomas Richard <thomas.richard@bootlin.com>
Link: https://github.com/openwrt/openwrt/pull/21413
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
This commit is contained in:
Thomas Richard 2026-01-05 13:54:42 +01:00 • committed by Hauke Mehrtens
parent 2530c99981
commit 9a584c631e
1 changed files with 35 additions and 0 deletions
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35
config/Config-kernel.in
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@ -413,6 +413,41 @@ config KERNEL_PREEMPT_TRACER
enabled. This option and the irqs-off timing option can be
used together or separately.)
config KERNEL_HWLAT_TRACER
bool "Tracer to detect hardware latencies (like SMIs)"
depends on KERNEL_FTRACE
help
This tracer, when enabled will create one or more kernel threads,
depending on what the cpumask file is set to, which each thread
spinning in a loop looking for interruptions caused by
something other than the kernel. For example, if a
System Management Interrupt (SMI) takes a noticeable amount of
time, this tracer will detect it. This is useful for testing
if a system is reliable for Real Time tasks.
Some files are created in the tracing directory when this
is enabled:
hwlat_detector/width - time in usecs for how long to spin for
hwlat_detector/window - time in usecs between the start of each
iteration
A kernel thread is created that will spin with interrupts disabled
for "width" microseconds in every "window" cycle. It will not spin
for "window - width" microseconds, where the system can
continue to operate.
The output will appear in the trace and trace_pipe files.
When the tracer is not running, it has no affect on the system,
but when it is running, it can cause the system to be
periodically non responsive. Do not run this tracer on a
production system.
To enable this tracer, echo in "hwlat" into the current_tracer
file. Every time a latency is greater than tracing_thresh, it will
be recorded into the ring buffer.
config KERNEL_HIST_TRIGGERS
bool "Histogram triggers"
depends on KERNEL_FTRACE