diff options
| author | Dave Hansen | 2013-06-21 08:51:38 -0700 |
|---|---|---|
| committer | Ingo Molnar | 2013-06-23 11:52:58 +0200 |
| commit | 0c4df02d739fed5ab081b330d67403206dd3967e (patch) | |
| tree | 37296c48ff5adef1537fd5c64977a3c1a0e8cff2 /Documentation/trace | |
| parent | 14c63f17b1fde5a575a28e96547a22b451c71fb5 (diff) | |
x86: Add NMI duration tracepoints
This patch has been invaluable in my adventures finding
issues in the perf NMI handler. I'm as big a fan of
printk() as anybody is, but using printk() in NMIs is
deadly when they're happening frequently.
Even hacking in trace_printk() ended up eating enough
CPU to throw off some of the measurements I was making.
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: paulus@samba.org
Cc: acme@ghostprotocols.net
Cc: Dave Hansen <dave@sr71.net>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'Documentation/trace')
| -rw-r--r-- | Documentation/trace/events-nmi.txt | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/Documentation/trace/events-nmi.txt b/Documentation/trace/events-nmi.txt new file mode 100644 index 000000000000..c03c8c89f08d --- /dev/null +++ b/Documentation/trace/events-nmi.txt @@ -0,0 +1,43 @@ +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 + |