perf diff: Support --cpu filter option

To improve 'perf diff', implement a --cpu filter option.

Multiple CPUs can be provided as a comma-separated list with no space:
0,1.  Ranges of CPUs are specified with -: 0-2. Default is to report
samples on all CPUs.

For example,

  perf diff --cpu 0,1

It only diff the samples for CPU0 and CPU1.
Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@intel.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1551791143-10334-3-git-send-email-yao.jin@linux.intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-diff.txt

@@ -163,6 +163,11 @@ OPTIONS
 	the end of perf.data.old and analyzes the perf.data from the
 	timestamp 3971.150589 to the end of perf.data.
 
+--cpu:: Only diff samples for the list of CPUs provided. Multiple CPUs can
+	be provided as a comma-separated list with no space: 0,1. Ranges of
+	CPUs are specified with -: 0-2. Default is to report samples on all
+	CPUs.
+
 COMPARISON
 ----------
 The comparison is governed by the baseline file. The baseline perf.data

tools/perf/builtin-diff.c

@@ -83,6 +83,9 @@ static unsigned int sort_compute = 1;
 static s64 compute_wdiff_w1;
 static s64 compute_wdiff_w2;
 
+static const char		*cpu_list;
+static DECLARE_BITMAP(cpu_bitmap, MAX_NR_CPUS);
+
 enum {
 	COMPUTE_DELTA,
 	COMPUTE_RATIO,
@@ -354,6 +357,11 @@ static int diff__process_sample_event(struct perf_tool *tool,
 		return -1;
 	}
 
+	if (cpu_list && !test_bit(sample->cpu, cpu_bitmap)) {
+		ret = 0;
+		goto out_put;
+	}
+
 	if (!hists__add_entry(hists, &al, NULL, NULL, NULL, sample, true)) {
 		pr_warning("problem incrementing symbol period, skipping event\n");
 		goto out_put;
@@ -892,6 +900,13 @@ static int __cmd_diff(void)
 				goto out_delete;
 		}
 
+		if (cpu_list) {
+			ret = perf_session__cpu_bitmap(d->session, cpu_list,
+						       cpu_bitmap);
+			if (ret < 0)
+				goto out_delete;
+		}
+
 		ret = perf_session__process_events(d->session);
 		if (ret) {
 			pr_err("Failed to process %s\n", d->data.path);
@@ -969,6 +984,7 @@ static const struct option options[] = {
 		     "How to display percentage of filtered entries", parse_filter_percentage),
 	OPT_STRING(0, "time", &pdiff.time_str, "str",
 		   "Time span (time percent or absolute timestamp)"),
+	OPT_STRING(0, "cpu", &cpu_list, "cpu", "list of cpus to profile"),
 	OPT_END()
 };