perf top: Add --max-stack option to limit callchain stack scan

When the callgraph function is enabled (-G), it may take a long time to
scan all the stack data and merge them accordingly.

This patch adds a new --max-stack option to perf-top to limit the depth
of callchain stack data to look at to reduce the time it takes for
perf-top to finish its processing. It reduces the amount of information
provided to the user in exchange for faster speed.

Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Acked-by: David Ahern <dsahern@gmail.com>
Tested-by: Davidlohr Bueso <davidlohr@hp.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1382107129-2010-5-git-send-email-Waiman.Long@hp.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/tools/perf/Documentation/perf-top.txt b/tools/perf/Documentation/perf-top.txt
index f65777c1f723..c16a09e2f182 100644
--- a/tools/perf/Documentation/perf-top.txt
+++ b/tools/perf/Documentation/perf-top.txt
@@ -158,6 +158,14 @@ Default is to monitor all CPUS.
 
 	Default: fractal,0.5,callee.
 
+--max-stack::
+	Set the stack depth limit when parsing the callchain, anything
+	beyond the specified depth will be ignored. This is a trade-off
+	between information loss and faster processing especially for
+	workloads that can have a very long callchain stack.
+
+	Default: 127
+
 --ignore-callees=<regex>::
         Ignore callees of the function(s) matching the given regex.
         This has the effect of collecting the callers of each such