mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
synced 2024-12-29 17:22:07 +00:00
2abfcd293b
The canonical location for the tracefs filesystem is at /sys/kernel/tracing. But, from Documentation/trace/ftrace.rst: Before 4.1, all ftrace tracing control files were within the debugfs file system, which is typically located at /sys/kernel/debug/tracing. For backward compatibility, when mounting the debugfs file system, the tracefs file system will be automatically mounted at: /sys/kernel/debug/tracing Many parts of Documentation still reference this older debugfs path, so let's update them to avoid confusion. Signed-off-by: Ross Zwisler <zwisler@google.com> Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org> Link: https://lore.kernel.org/r/20230125213251.2013791-1-zwisler@google.com Signed-off-by: Jonathan Corbet <corbet@lwn.net>
46 lines
1.6 KiB
ReStructuredText
46 lines
1.6 KiB
ReStructuredText
================
|
|
NMI Trace Events
|
|
================
|
|
|
|
These events normally show up here:
|
|
|
|
/sys/kernel/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/tracing/events/nmi/nmi_handler
|
|
echo 'handler==0xffffffff81625600 && delta_ns>1000000' > filter
|
|
echo 1 > enable
|
|
|
|
Your output would then look like::
|
|
|
|
$ cat /sys/kernel/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
|
|
|