perf intel-pt: Document snapshot control command

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

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lore.kernel.org/lkml/20200901093758.32293-7-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/Documentation/perf-intel-pt.txt b/tools/perf/Documentation/perf-intel-pt.txt
index d5a266d..cb637e0 100644 (file)
--- 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