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>

3 files changed, 15 insertions, 2 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
diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 112cb7d68e64..386d83324a8d 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -771,7 +771,7 @@ static void perf_event__process_sample(struct perf_tool *tool,
                         err = machine__resolve_callchain(machine, evsel,
                                                          al.thread, sample,
                                                          &parent, &al,
-                                                         PERF_MAX_STACK_DEPTH);
+                                                         top->max_stack);
                         if (err)
                                 return;
                 }
@@ -1048,10 +1048,11 @@ int cmd_top(int argc, const char **argv, const char *prefix __maybe_unused)
                         .user_freq      = UINT_MAX,
                         .user_interval  = ULLONG_MAX,
                         .freq           = 4000, /* 4 KHz */
-                        .target              = {
+                        .target         = {
                                 .uses_mmap   = true,
                         },
                 },
+                .max_stack           = PERF_MAX_STACK_DEPTH,
                 .sym_pcnt_filter     = 5,
         };
         struct perf_record_opts *opts = &top.record_opts;
@@ -1110,6 +1111,9 @@ int cmd_top(int argc, const char **argv, const char *prefix __maybe_unused)
         OPT_CALLBACK_DEFAULT('G', "call-graph", &top.record_opts,
                              "mode[,dump_size]", record_callchain_help,
                              &parse_callchain_opt, "fp"),
+        OPT_INTEGER(0, "max-stack", &top.max_stack,
+                    "Set the maximum stack depth when parsing the callchain. "
+                    "Default: " __stringify(PERF_MAX_STACK_DEPTH)),
         OPT_CALLBACK(0, "ignore-callees", NULL, "regex",
                    "ignore callees of these functions in call graphs",
                    report_parse_ignore_callees_opt),
diff --git a/tools/perf/util/top.h b/tools/perf/util/top.h
index b554ffc462b6..88cfeaff600b 100644
--- a/tools/perf/util/top.h
+++ b/tools/perf/util/top.h
@@ -24,6 +24,7 @@ struct perf_top {
         u64                exact_samples;
         u64                guest_us_samples, guest_kernel_samples;
         int                print_entries, count_filter, delay_secs;
+        int                max_stack;
         bool               hide_kernel_symbols, hide_user_symbols, zero;
         bool               use_tui, use_stdio;
         bool               kptr_restrict_warned;