Re: [PATCH 1/3] perf, tools: Add support for skipping itrace instructions

[Adrian Hunter <adrian.hunter@intel.com>]

On 01/03/16 01:05, Andi Kleen wrote:
> From: Andi Kleen <ak@linux.intel.com>
> 
> 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.
> 
> Cc: Adrian Hunter <adrian.hunter@intel.com>
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
> ---
>  tools/perf/Documentation/intel-pt.txt |  7 +++++++
>  tools/perf/util/auxtrace.c            |  7 +++++++
>  tools/perf/util/auxtrace.h            |  2 ++
>  tools/perf/util/intel-pt.c            | 14 ++++++++++++--
>  4 files changed, 28 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/Documentation/intel-pt.txt b/tools/perf/Documentation/intel-pt.txt
> index be764f9..c6c8318 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
>  -----------

Also need to update tools/perf/Documentation/itrace.txt

> diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c
> index 360fda0..a013c1f 100644
> --- a/tools/perf/util/auxtrace.c
> +++ b/tools/perf/util/auxtrace.c
> @@ -939,6 +939,7 @@ 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;
>  }
>  
>  /*
> @@ -1063,6 +1064,12 @@ 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 b86f90db..235d3c3 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-pt.c b/tools/perf/util/intel-pt.c
> index 05d8158..a0c5e7d 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)

The '>' looks the wrong way around

> +		return 0;
> +

For consistency, wouldn't it be better to do it this way for "instructions"
and "transactions" too. i.e. in intel_pt_synth_instruction_sample() and
intel_pt_synth_transaction_sample()

>  	event->sample.header.type = PERF_RECORD_SAMPLE;
>  	event->sample.header.misc = PERF_RECORD_MISC_USER;
>  	event->sample.header.size = sizeof(struct perf_event_header);
> @@ -1196,14 +1202,18 @@ 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;
> 

The BTS code is almost the same, so I would suggest doing BTS as well as PT.
i.e.

diff --git a/tools/perf/util/intel-bts.c b/tools/perf/util/intel-bts.c
index eb0e7f8bf515..e3cc1057a097 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);