perf tools: Add support for skipping itrace instructions

When using 'perf script' to look at PT traces it is often useful to
ignore the initialization code at the beginning.

On larger traces which may have many millions of instructions in
initialization code doing that in a pipeline can be very slow, with perf
script spending a lot of CPU time calling printf and writing data.

This patch adds an extension to the --itrace argument that skips 'n'
events (instructions, branches or transactions) at the beginning. This
is much more efficient.

v2:
Add support for BTS (Adrian Hunter)
Document in itrace.txt
Fix branch check
Check transactions and instructions too

Committer note:

To test intel_pt one needs to make sure VT-x isn't active, i.e.
stopping KVM guests on the test machine, as described by Andi Kleen
at http://lkml.kernel.org/r/20160301234953.GD23621@tassilo.jf.intel.com

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1459187142-20035-1-git-send-email-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

6 files changed, 49 insertions, 2 deletions

diff --git a/tools/perf/Documentation/intel-pt.txt b/tools/perf/Documentation/intel-pt.txt
index be764f9ec769..c6c8318e38a2 100644
--- a/tools/perf/Documentation/intel-pt.txt
+++ b/tools/perf/Documentation/intel-pt.txt
@@ -672,6 +672,7 @@ The letters are:
 	d	create a debug log
 	g	synthesize a call chain (use with i or x)
 	l	synthesize last branch entries (use with i or x)
+	s	skip initial number of events
 
 "Instructions" events look like they were recorded by "perf record -e
 instructions".
@@ -730,6 +731,12 @@ from one sample to the next.
 
 To disable trace decoding entirely, use the option --no-itrace.
 
+It is also possible to skip events generated (instructions, branches, transactions)
+at the beginning. This is useful to ignore initialization code.
+
+	--itrace=i0nss1000000
+
+skips the first million instructions.
 
 dump option
 -----------
diff --git a/tools/perf/Documentation/itrace.txt b/tools/perf/Documentation/itrace.txt
index 65453f4c7006..e2a4c5e0dbe5 100644
--- a/tools/perf/Documentation/itrace.txt
+++ b/tools/perf/Documentation/itrace.txt
@@ -7,6 +7,7 @@
 		d	create a debug log
 		g	synthesize a call chain (use with i or x)
 		l	synthesize last branch entries (use with i or x)
+		s       skip initial number of events
 
 	The default is all events i.e. the same as --itrace=ibxe
 
@@ -24,3 +25,10 @@
 
 	Also the number of last branch entries (default 64, max. 1024) for
 	instructions or transactions events can be specified.
+
+	It is also possible to skip events generated (instructions, branches, transactions)
+	at the beginning. This is useful to ignore initialization code.
+
+	--itrace=i0nss1000000
+
+	skips the first million instructions.
diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c
index ec164fe70718..c9169011e55e 100644
--- a/tools/perf/util/auxtrace.c
+++ b/tools/perf/util/auxtrace.c
@@ -940,6 +940,7 @@ void itrace_synth_opts__set_default(struct itrace_synth_opts *synth_opts)
 	synth_opts->period = PERF_ITRACE_DEFAULT_PERIOD;
 	synth_opts->callchain_sz = PERF_ITRACE_DEFAULT_CALLCHAIN_SZ;
 	synth_opts->last_branch_sz = PERF_ITRACE_DEFAULT_LAST_BRANCH_SZ;
+	synth_opts->initial_skip = 0;
 }
 
 /*
@@ -1064,6 +1065,12 @@ int itrace_parse_synth_opts(const struct option *opt, const char *str,
 				synth_opts->last_branch_sz = val;
 			}
 			break;
+		case 's':
+			synth_opts->initial_skip = strtoul(p, &endptr, 10);
+			if (p == endptr)
+				goto out_err;
+			p = endptr;
+			break;
 		case ' ':
 		case ',':
 			break;
diff --git a/tools/perf/util/auxtrace.h b/tools/perf/util/auxtrace.h
index 57ff31ecb8e4..767989e0e312 100644
--- a/tools/perf/util/auxtrace.h
+++ b/tools/perf/util/auxtrace.h
@@ -68,6 +68,7 @@ enum itrace_period_type {
  * @last_branch_sz: branch context size
  * @period: 'instructions' events period
  * @period_type: 'instructions' events period type
+ * @initial_skip: skip N events at the beginning.
  */
 struct itrace_synth_opts {
 	bool			set;
@@ -86,6 +87,7 @@ struct itrace_synth_opts {
 	unsigned int		last_branch_sz;
 	unsigned long long	period;
 	enum itrace_period_type	period_type;
+	unsigned long		initial_skip;
 };
 
 /**
diff --git a/tools/perf/util/intel-bts.c b/tools/perf/util/intel-bts.c
index abf1366e2a24..9df996085563 100644
--- a/tools/perf/util/intel-bts.c
+++ b/tools/perf/util/intel-bts.c
@@ -66,6 +66,7 @@ struct intel_bts {
 	u64				branches_id;
 	size_t				branches_event_size;
 	bool				synth_needs_swap;
+	unsigned long			num_events;
 };
 
 struct intel_bts_queue {
@@ -275,6 +276,10 @@ static int intel_bts_synth_branch_sample(struct intel_bts_queue *btsq,
 	union perf_event event;
 	struct perf_sample sample = { .ip = 0, };
 
+	if (bts->synth_opts.initial_skip &&
+	    bts->num_events++ <= bts->synth_opts.initial_skip)
+		return 0;
+
 	event.sample.header.type = PERF_RECORD_SAMPLE;
 	event.sample.header.misc = PERF_RECORD_MISC_USER;
 	event.sample.header.size = sizeof(struct perf_event_header);
diff --git a/tools/perf/util/intel-pt.c b/tools/perf/util/intel-pt.c
index 407f11b97c8d..ddec87f6e616 100644
--- a/tools/perf/util/intel-pt.c
+++ b/tools/perf/util/intel-pt.c
@@ -100,6 +100,8 @@ struct intel_pt {
 	u64 cyc_bit;
 	u64 noretcomp_bit;
 	unsigned max_non_turbo_ratio;
+
+	unsigned long num_events;
 };
 
 enum switch_state {
@@ -972,6 +974,10 @@ static int intel_pt_synth_branch_sample(struct intel_pt_queue *ptq)
 	if (pt->branches_filter && !(pt->branches_filter & ptq->flags))
 		return 0;
 
+	if (pt->synth_opts.initial_skip &&
+	    pt->num_events++ < pt->synth_opts.initial_skip)
+		return 0;
+
 	event->sample.header.type = PERF_RECORD_SAMPLE;
 	event->sample.header.misc = PERF_RECORD_MISC_USER;
 	event->sample.header.size = sizeof(struct perf_event_header);
@@ -1029,6 +1035,10 @@ static int intel_pt_synth_instruction_sample(struct intel_pt_queue *ptq)
 	union perf_event *event = ptq->event_buf;
 	struct perf_sample sample = { .ip = 0, };
 
+	if (pt->synth_opts.initial_skip &&
+	    pt->num_events++ < pt->synth_opts.initial_skip)
+		return 0;
+
 	event->sample.header.type = PERF_RECORD_SAMPLE;
 	event->sample.header.misc = PERF_RECORD_MISC_USER;
 	event->sample.header.size = sizeof(struct perf_event_header);
@@ -1087,6 +1097,10 @@ static int intel_pt_synth_transaction_sample(struct intel_pt_queue *ptq)
 	union perf_event *event = ptq->event_buf;
 	struct perf_sample sample = { .ip = 0, };
 
+	if (pt->synth_opts.initial_skip &&
+	    pt->num_events++ < pt->synth_opts.initial_skip)
+		return 0;
+
 	event->sample.header.type = PERF_RECORD_SAMPLE;
 	event->sample.header.misc = PERF_RECORD_MISC_USER;
 	event->sample.header.size = sizeof(struct perf_event_header);
@@ -1199,14 +1213,18 @@ static int intel_pt_sample(struct intel_pt_queue *ptq)
 	ptq->have_sample = false;
 
 	if (pt->sample_instructions &&
-	    (state->type & INTEL_PT_INSTRUCTION)) {
+	    (state->type & INTEL_PT_INSTRUCTION) &&
+	    (!pt->synth_opts.initial_skip ||
+	     pt->num_events++ >= pt->synth_opts.initial_skip)) {
 		err = intel_pt_synth_instruction_sample(ptq);
 		if (err)
 			return err;
 	}
 
 	if (pt->sample_transactions &&
-	    (state->type & INTEL_PT_TRANSACTION)) {
+	    (state->type & INTEL_PT_TRANSACTION) &&
+	    (!pt->synth_opts.initial_skip ||
+	     pt->num_events++ >= pt->synth_opts.initial_skip)) {
 		err = intel_pt_synth_transaction_sample(ptq);
 		if (err)
 			return err;