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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 10:05:51 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 10:05:51 +0000
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Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+================
+NMI Trace Events
+================
+
+These events normally show up here:
+
+ /sys/kernel/debug/tracing/events/nmi
+
+
+nmi_handler
+-----------
+
+You might want to use this tracepoint if you suspect that your
+NMI handlers are hogging large amounts of CPU time. The kernel
+will warn if it sees long-running handlers::
+
+ INFO: NMI handler took too long to run: 9.207 msecs
+
+and this tracepoint will allow you to drill down and get some
+more details.
+
+Let's say you suspect that perf_event_nmi_handler() is causing
+you some problems and you only want to trace that handler
+specifically. You need to find its address::
+
+ $ grep perf_event_nmi_handler /proc/kallsyms
+ ffffffff81625600 t perf_event_nmi_handler
+
+Let's also say you are only interested in when that function is
+really hogging a lot of CPU time, like a millisecond at a time.
+Note that the kernel's output is in milliseconds, but the input
+to the filter is in nanoseconds! You can filter on 'delta_ns'::
+
+ cd /sys/kernel/debug/tracing/events/nmi/nmi_handler
+ echo 'handler==0xffffffff81625600 && delta_ns>1000000' > filter
+ echo 1 > enable
+
+Your output would then look like::
+
+ $ cat /sys/kernel/debug/tracing/trace_pipe
+ <idle>-0 [000] d.h3 505.397558: nmi_handler: perf_event_nmi_handler() delta_ns: 3236765 handled: 1
+ <idle>-0 [000] d.h3 505.805893: nmi_handler: perf_event_nmi_handler() delta_ns: 3174234 handled: 1
+ <idle>-0 [000] d.h3 506.158206: nmi_handler: perf_event_nmi_handler() delta_ns: 3084642 handled: 1
+ <idle>-0 [000] d.h3 506.334346: nmi_handler: perf_event_nmi_handler() delta_ns: 3080351 handled: 1
+