[PATCH V2 6/6] perf intel-pt: Document snapshot control command

Adrian Hunter
2020-09-01T09:38:59Z

The documentation descibes snapshot mode. Update it to include the new
snapshot control command.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
tools/perf/Documentation/perf-intel-pt.txt | 23 +++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/tools/perf/Documentation/perf-intel-pt.txt b/tools/perf/Documentation/perf-intel-pt.txt
index d5a266d7f15b..cb637e0d0743 100644
--- a/tools/perf/Documentation/perf-intel-pt.txt
+++ b/tools/perf/Documentation/perf-intel-pt.txt
@@ -558,7 +558,7 @@ The mmap size and auxtrace mmap size are displayed if the -vv option is used e.g
Intel PT modes of operation
~~~~~~~~~~~~~~~~~~~~~~~~~~~

-Intel PT can be used in 2 modes:
+Intel PT can be used in 3 modes:
full-trace mode
sample mode
snapshot mode
@@ -571,7 +571,8 @@ Sample mode attaches a Intel PT sample to other events e.g.

perf record --aux-sample -e intel_pt//u -e branch-misses:u

-Snapshot mode captures the available data when a signal is sent e.g.
+Snapshot mode captures the available data when a signal is sent or "snapshot"
+control command is issued. e.g. using a signal

perf record -v -e intel_pt//u -S ./loopy 1000000000 &
[1] 11435
@@ -582,7 +583,23 @@ Note that the signal sent is SIGUSR2.
Note that "Recording AUX area tracing snapshot" is displayed because the -v
option is used.

-The 2 modes cannot be used together.
+The advantage of using "snapshot" control command is that the access is
+controlled by access to a FIFO e.g.
+
+ $ mkfifo perf.control
+ $ mkfifo perf.ack
+ $ cat perf.ack &
+ [1] 15235
+ $ sudo ~/bin/perf record --control fifo:perf.control,perf.ack -S -e intel_pt//u -- sleep 60 &
+ [2] 15243
+ $ ps -e | grep perf
+ 15244 pts/1 00:00:00 perf
+ $ kill -USR2 15244
+ bash: kill: (15244) - Operation not permitted
+ $ echo snapshot > perf.control
+ ack
+
+The 3 Intel PT modes of operation cannot be used together.

Buffer handling
--
2.17.1