Re: [PATCH 15/15] perf tools: Support spark lines in perf stat

[Ingo Molnar]

* Jiri Olsa <jolsa@xxxxxxxxxx> wrote:

> From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> 
> perf stat -rX prints the stddev for multiple measurements.

Call it "--repeat X", that's how most people know it.

> Just looking at the stddev for judging the quality of the data
> is a bit dangerous The simplest sanity check is to just look

"Dangerous?". Unexplained FUD. Also a missing perid.

> at a simple plot. This patchs add a sparkline to the end
> of the measurements to make it simple to judge the data.

Should explain what a 'sparkline' is when it's first mentioned, not 2 
sentences later.

> The sparkline only uses UTF-8, so should be readable
> in all modern tools and terminals.
> 
> The sparkline is between the minimum and maximum of the data,
> so it's mainly a indicator of variance. To keep the code
> simple and make the output not too wide only the first
> 8 values are printed. If more values are there it adds '..'
> 
> The code is inspired by Zach Holman's spark shell script.

Zach Holman should be on Cc:.

> Example output (view in non-proportial font):
> 
>  Performance counter stats for 'true' (10 runs):
> 
>           0.175672      task-clock (msec)         #    0.555 CPUs utilized            ( +-  1.77% ) ââââââââ..
>                  0      context-switches          #    0.000 K/sec
>                  0      cpu-migrations            #    0.000 K/sec
>                114      page-faults               #    0.647 M/sec                    ( +-  0.14% ) ââââââââ..
>            520,798      cycles                    #    2.965 GHz                      ( +-  1.75% ) ââââââââ..
>            433,525      instructions              #    0.83  insns per cycle          ( +-  0.28% ) ââââââââ..
>             83,012      branches                  #  472.537 M/sec                    ( +-  0.31% ) ââââââââ..
>              3,157      branch-misses             #    3.80% of all branches          ( +-  2.55% ) ââââââââ..
> 
>        0.000316660 seconds time elapsed                                          ( +-  1.78% ) ââââââââ..

The noise data is not aligned vertically in the changelog - is it in 
the real code? It should be.

> As you can see even in the most simple run there are quite 
> interesting patterns. The time sparkline suggests it would be also 
> useful to have an option to throw the first measurement away.

First two should be thrown away, probably, to reduce the resulting 
stddev.

> Known issues:
> - Makes the perf stat output wider. Could be adjust by shrinking
> some white space. Not done so far.
> - No output for -A/--per-socket/--per-core with -rX. This code
> is missing the basic noise detection code. Once it's added there
> sparklines could be shown too.

The feauture looks useful, but at minimum the second shortcoming 
should be fixed first in a separate patch, before applying new 
features and further complicating the code.

> Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Link: http://lkml.kernel.org/r/1401838086-17750-1-git-send-email-andi@xxxxxxxxxxxxxx
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  tools/perf/Documentation/perf-stat.txt |  4 ++++
>  tools/perf/Makefile.perf               |  1 +
>  tools/perf/builtin-stat.c              | 12 ++++++++++++
>  tools/perf/util/spark.c                | 31 +++++++++++++++++++++++++++++++
>  tools/perf/util/spark.h                |  4 ++++
>  tools/perf/util/stat.c                 | 34 ++++++++++++++++++++++++++++++++++
>  tools/perf/util/stat.h                 | 10 ++++++++++
>  7 files changed, 96 insertions(+)
>  create mode 100644 tools/perf/util/spark.c
>  create mode 100644 tools/perf/util/spark.h
> 
> diff --git a/tools/perf/Documentation/perf-stat.txt b/tools/perf/Documentation/perf-stat.txt
> index 29ee857..840c1db 100644
> --- a/tools/perf/Documentation/perf-stat.txt
> +++ b/tools/perf/Documentation/perf-stat.txt
> @@ -53,6 +53,10 @@ OPTIONS
>  -r::
>  --repeat=<n>::
>  	repeat command and print average + stddev (max: 100). 0 means forever.
> +	In addition it prints a spark line (when not in CSV mode), which visualizes the
> +	variance between minimum and maximum of the measurements. This allows a simple sanity
> +	check of the measurements. Only 8 values are printed, when more are available
> +	it adds ..
>  
>  -B::
>  --big-num::
> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> index 9670a16..90b3aa7 100644
> --- a/tools/perf/Makefile.perf
> +++ b/tools/perf/Makefile.perf
> @@ -359,6 +359,7 @@ LIB_OBJS += $(OUTPUT)util/trace-event-scripting.o
>  LIB_OBJS += $(OUTPUT)util/trace-event.o
>  LIB_OBJS += $(OUTPUT)util/svghelper.o
>  LIB_OBJS += $(OUTPUT)util/sort.o
> +LIB_OBJS += $(OUTPUT)util/spark.o
>  LIB_OBJS += $(OUTPUT)util/hist.o
>  LIB_OBJS += $(OUTPUT)util/probe-event.o
>  LIB_OBJS += $(OUTPUT)util/util.o
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index 65a151e..cb0f7c5 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -1176,6 +1176,9 @@ static void print_aggr(char *prefix)
>  				if (run != ena)
>  					fprintf(output, "  (%.2f%%)",
>  						100.0 * run / ena);
> +
> +				fputc(' ', output);
> +				print_stat_spark(output, counter->priv);
>  			}
>  			fputc('\n', output);
>  		}
> @@ -1229,6 +1232,9 @@ static void print_counter_aggr(struct perf_evsel *counter, char *prefix)
>  		return;
>  	}
>  
> +	fputc(' ', output);
> +	print_stat_spark(output, counter->priv);
> +
>  	if (scaled) {
>  		double avg_enabled, avg_running;
>  
> @@ -1295,6 +1301,9 @@ static void print_counter(struct perf_evsel *counter, char *prefix)
>  			if (run != ena)
>  				fprintf(output, "  (%.2f%%)",
>  					100.0 * run / ena);
> +
> +			fputc(' ', output);
> +			print_stat_spark(output, counter->priv);
>  		}
>  		fputc('\n', output);
>  	}
> @@ -1355,6 +1364,9 @@ static void print_stat(int argc, const char **argv)
>  			fprintf(output, "                                        ");
>  			print_noise_pct(stddev_stats(&walltime_nsecs_stats),
>  					avg_stats(&walltime_nsecs_stats));
> +
> +			fputc(' ', output);
> +			print_stat_spark(output, &walltime_nsecs_stats);


Why is that 2-line pattern repeated 4 times?

>  		}
>  		fprintf(output, "\n\n");
>  	}
> diff --git a/tools/perf/util/spark.c b/tools/perf/util/spark.c
> new file mode 100644
> index 0000000..5a1033f
> --- /dev/null
> +++ b/tools/perf/util/spark.c
> @@ -0,0 +1,31 @@
> +#include <stdio.h>
> +#include <limits.h>
> +#include "spark.h"
> +
> +#define NUM_SPARKS 8
> +#define SPARK_SHIFT 8
> +
> +/* Print spark lines on outf for numval values in val. */
> +void print_spark(FILE *outf, unsigned long long *val, int numval)

The output file is called 'output' in the calling context, there's no 
reason to randomly depart from that convention and introduce a random 
new one: not a single existing line in tools/perf/ calls an output 
file 'outf'.

Also, I don't see 'numval' used anywhere in perf. The canonical naming 
would be different.

> +{
> +	static const char *ticks[NUM_SPARKS] = {
> +		"â",  "â", "â", "â", "â", "â", "â", "â"
> +	};
> +	int i;
> +	unsigned long long min = ULLONG_MAX, max = 0, f;

min/max is a somewhat sloppy name as well (easy to confuse with 
min()/max()), should be somehing like min_val/max_val, which is in 
line .

> +
> +	for (i = 0; i < numval; i++) {
> +		if (val[i] < min)
> +			min = val[i];
> +		if (val[i] > max)
> +			max = val[i];
> +	}
> +	f = ((max - min) << SPARK_SHIFT) / (NUM_SPARKS - 1);
> +	if (f < 1)
> +		f = 1;
> +	for (i = 0; i < numval; i++) {
> +		int index = ((val[i] - min) << SPARK_SHIFT) / f;
> +		if (index >= 0 && index < NUM_SPARKS)
> +			fputs(ticks[index], outf);

That's not primarily an 'index', it's an indexed 'variance' value. So 
'variance_idx' or so.

> +	}
> +}
> diff --git a/tools/perf/util/spark.h b/tools/perf/util/spark.h
> new file mode 100644
> index 0000000..d9ebc94
> --- /dev/null
> +++ b/tools/perf/util/spark.h
> @@ -0,0 +1,4 @@
> +#ifndef SPARK_H
> +#define SPARK_H 1
> +void print_spark(FILE *outf, unsigned long long *val, int numval);
> +#endif
> diff --git a/tools/perf/util/stat.c b/tools/perf/util/stat.c
> index 6506b3d..a7c02c5 100644
> --- a/tools/perf/util/stat.c
> +++ b/tools/perf/util/stat.c
> @@ -1,10 +1,16 @@
>  #include <math.h>
> +#include <stdio.h>
>  
>  #include "stat.h"
> +#include "spark.h"
>  
>  void update_stats(struct stats *stats, u64 val)
>  {
>  	double delta;
> +	int n = stats->n;
> +
> +	if (n < NUM_SPARK_VALS)
> +		stats->svals[n] = val;
>  
>  	stats->n++;
>  	delta = val - stats->mean;
>	stats->mean += delta / stats->n;

It is absolutely sloppy, potentially misleading and unrobust to put an 
integer rounded value of 'double n' into a local variable named 'int 
n' ...

> @@ -61,3 +67,31 @@ double rel_stddev_stats(double stddev, double avg)
>  
>  	return pct;
>  }
> +
> +static int all_zero(unsigned long long *vals, int len)
> +{
> +	int i;
> +
> +	for (i = 0; i < len; i++)
> +		if (vals[i] != 0)
> +			return 0;
> +	return 1;
> +}
> +
> +void print_stat_spark(FILE *f, struct stats *stat)
> +{
> +	int len;
> +
> +	if (stat->n <= 1)
> +		return;
> +
> +	len = stat->n;
> +	if (len > NUM_SPARK_VALS)
> +		len = NUM_SPARK_VALS;
> +	if (all_zero(stat->svals, len))
> +		return;
> +
> +	print_spark(f, stat->svals, len);
> +	if (stat->n > NUM_SPARK_VALS)
> +		fputs("..", f);
> +}
> diff --git a/tools/perf/util/stat.h b/tools/perf/util/stat.h
> index 5667fc3..a049f03 100644
> --- a/tools/perf/util/stat.h
> +++ b/tools/perf/util/stat.h
> @@ -1,12 +1,16 @@
>  #ifndef __PERF_STATS_H
>  #define __PERF_STATS_H
>  
> +#include <stdio.h>
>  #include <linux/types.h>
>  
> +#define NUM_SPARK_VALS 8 /* support spark line on first N items */
> +
>  struct stats
>  {
>  	double n, mean, M2;
>  	u64 max, min;
> +	unsigned long long svals[NUM_SPARK_VALS];
>  };

The structure's increasing size justifies proper vertical alignment.

>  
>  void update_stats(struct stats *stats, u64 val);
> @@ -14,12 +18,18 @@ double avg_stats(struct stats *stats);
>  double stddev_stats(struct stats *stats);
>  double rel_stddev_stats(double stddev, double avg);
>  
> +void print_stat_spark(FILE *f, struct stats *stat);
> +
>  static inline void init_stats(struct stats *stats)
>  {
> +	int i;
> +
>  	stats->n    = 0.0;
>  	stats->mean = 0.0;
>  	stats->M2   = 0.0;
>  	stats->min  = (u64) -1;
>  	stats->max  = 0;
> +	for (i = 0; i < NUM_SPARK_VALS; i++)
> +		stats->svals[i] = 0;

memset(), or introduce a new helper, memclear_struct():

 #define memclear_struct(struct_ptr) memset(struct_ptr, 0, sizeof(*(struct_ptr)))

Also, init_stats() should now probably move into util/stat.c. (in a 
separate patch preparing these changes.)

Thanks,

	Ingo
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