[PATCH v6] perf diff: Report noisy for cycles diff

From: Jin Yao
Date: Tue Aug 20 2019 - 08:22:53 EST

This patch prints the stddev and hist for the cycles diff of
program block. It can help us to understand if the cycles
is noisy or not.

This patch is inspired by Andi Kleen's patch
https://lwn.net/Articles/600471/

We create new option '--cycles-hist'.

Example:

perf record -b ./div
perf record -b ./div
perf diff -c cycles

# Baseline [Program Block Range] Cycles Diff Shared Object Symbol
# ........ ...................................................................... ................. ............................
#
46.72% [div.c:40 -> div.c:40] 0 div [.] main
46.72% [div.c:42 -> div.c:44] 0 div [.] main
46.72% [div.c:42 -> div.c:39] 0 div [.] main
20.54% [random_r.c:357 -> random_r.c:394] 1 libc-2.27.so [.] __random_r
20.54% [random_r.c:357 -> random_r.c:380] 0 libc-2.27.so [.] __random_r
20.54% [random_r.c:388 -> random_r.c:388] 0 libc-2.27.so [.] __random_r
20.54% [random_r.c:388 -> random_r.c:391] 0 libc-2.27.so [.] __random_r
17.04% [random.c:288 -> random.c:291] 0 libc-2.27.so [.] __random
17.04% [random.c:291 -> random.c:291] 0 libc-2.27.so [.] __random
17.04% [random.c:293 -> random.c:293] 0 libc-2.27.so [.] __random
17.04% [random.c:295 -> random.c:295] 0 libc-2.27.so [.] __random
17.04% [random.c:295 -> random.c:295] 0 libc-2.27.so [.] __random
17.04% [random.c:298 -> random.c:298] 0 libc-2.27.so [.] __random
8.40% [div.c:22 -> div.c:25] 0 div [.] compute_flag
8.40% [div.c:27 -> div.c:28] 0 div [.] compute_flag
5.14% [rand.c:26 -> rand.c:27] 0 libc-2.27.so [.] rand
5.14% [rand.c:28 -> rand.c:28] 0 libc-2.27.so [.] rand
2.15% [rand@plt+0 -> rand@plt+0] 0 div [.] rand@plt
0.00% [kernel.kallsyms] [k] __x86_indirect_thunk_rax
0.00% [do_mmap+714 -> do_mmap+732] -10 [kernel.kallsyms] [k] do_mmap
0.00% [do_mmap+737 -> do_mmap+765] 1 [kernel.kallsyms] [k] do_mmap
0.00% [do_mmap+262 -> do_mmap+299] 0 [kernel.kallsyms] [k] do_mmap
0.00% [__x86_indirect_thunk_r15+0 -> __x86_indirect_thunk_r15+0] 7 [kernel.kallsyms] [k] __x86_indirect_thunk_r15
0.00% [native_sched_clock+0 -> native_sched_clock+119] -1 [kernel.kallsyms] [k] native_sched_clock
0.00% [native_write_msr+0 -> native_write_msr+16] -13 [kernel.kallsyms] [k] native_write_msr

When we enable the option '--cycles-hist', the output is

perf diff -c cycles --cycles-hist

# Baseline [Program Block Range] Cycles Diff stddev/Hist Shared Object Symbol
# ........ ...................................................................... ................. ................. ............................
#
46.72% [div.c:40 -> div.c:40] 0 Â 37.8% ââââââââ div [.] main
46.72% [div.c:42 -> div.c:44] 0 Â 49.4% ââââââââ div [.] main
46.72% [div.c:42 -> div.c:39] 0 Â 24.1% ââââââââ div [.] main
20.54% [random_r.c:357 -> random_r.c:394] 1 Â 33.5% ââââââââ libc-2.27.so [.] __random_r
20.54% [random_r.c:357 -> random_r.c:380] 0 Â 39.4% ââââââââ libc-2.27.so [.] __random_r
20.54% [random_r.c:388 -> random_r.c:388] 0 libc-2.27.so [.] __random_r
20.54% [random_r.c:388 -> random_r.c:391] 0 Â 41.2% ââââââââ libc-2.27.so [.] __random_r
17.04% [random.c:288 -> random.c:291] 0 Â 48.8% ââââââââ libc-2.27.so [.] __random
17.04% [random.c:291 -> random.c:291] 0 Â100.0% ââââââââ libc-2.27.so [.] __random
17.04% [random.c:293 -> random.c:293] 0 Â100.0% ââââââââ libc-2.27.so [.] __random
17.04% [random.c:295 -> random.c:295] 0 Â100.0% ââââââââ libc-2.27.so [.] __random
17.04% [random.c:295 -> random.c:295] 0 libc-2.27.so [.] __random
17.04% [random.c:298 -> random.c:298] 0 Â 75.6% ââââââââ libc-2.27.so [.] __random
8.40% [div.c:22 -> div.c:25] 0 Â 42.1% ââââââââ div [.] compute_flag
8.40% [div.c:27 -> div.c:28] 0 Â 41.8% ââââââââ div [.] compute_flag
5.14% [rand.c:26 -> rand.c:27] 0 Â 37.8% ââââââââ libc-2.27.so [.] rand
5.14% [rand.c:28 -> rand.c:28] 0 libc-2.27.so [.] rand
2.15% [rand@plt+0 -> rand@plt+0] 0 div [.] rand@plt
0.00% [kernel.kallsyms] [k] __x86_indirect_thunk_rax
0.00% [do_mmap+714 -> do_mmap+732] -10 [kernel.kallsyms] [k] do_mmap
0.00% [do_mmap+737 -> do_mmap+765] 1 [kernel.kallsyms] [k] do_mmap
0.00% [do_mmap+262 -> do_mmap+299] 0 [kernel.kallsyms] [k] do_mmap
0.00% [__x86_indirect_thunk_r15+0 -> __x86_indirect_thunk_r15+0] 7 [kernel.kallsyms] [k] __x86_indirect_thunk_r15
0.00% [native_sched_clock+0 -> native_sched_clock+119] -1 Â 38.5% âââ [kernel.kallsyms] [k] native_sched_clock
0.00% [native_write_msr+0 -> native_write_msr+16] -13 Â 47.1% ââââââ [kernel.kallsyms] [k] native_write_msr

v6:
---
1. Jiri provides better code for using data__hpp_register() in ui_init().
Use this code in v6.

v5:
---
1. Refine the use of data__hpp_register() in ui_init() according to
Jiri's suggestion.

v4:
---
1. Rename the new option from '--noisy' to '--cycles-hist'
2. Remove the option '-n'.
3. Only update the spark value and stats when '--cycles-hist' is enabled.
4. Remove the code of printing '..'.

v3:
---
1. Move the histogram to a separate column
2. Move the svals[] out of struct stats

v2:
---
Jiri got a compile error,

CC builtin-diff.o
builtin-diff.c: In function âcompute_cycles_diffâ:
builtin-diff.c:712:10: error: taking the absolute value of unsigned type âu64â {aka âlong unsigned intâ} has no effect [-Werror=absolute-value]
712 | labs(pair->block_info->cycles_spark[i] -
| ^~~~

Because the result of u64 - u64 is still u64. Now we change the type of
cycles_spark[] to s64.

Signed-off-by: Jin Yao <yao.jin@xxxxxxxxxxxxxxx>
---
tools/perf/Documentation/perf-diff.txt | 5 +
tools/perf/builtin-diff.c | 143 +++++++++++++++++++++++++
tools/perf/util/Build | 1 +
tools/perf/util/annotate.c | 4 +
tools/perf/util/annotate.h | 2 +
tools/perf/util/sort.h | 4 +
tools/perf/util/spark.c | 34 ++++++
tools/perf/util/spark.h | 8 ++
tools/perf/util/symbol.h | 2 +
9 files changed, 203 insertions(+)
create mode 100644 tools/perf/util/spark.c
create mode 100644 tools/perf/util/spark.h

diff --git a/tools/perf/Documentation/perf-diff.txt b/tools/perf/Documentation/perf-diff.txt
index d5cc15e651cf..f50ca0fef0a4 100644
--- a/tools/perf/Documentation/perf-diff.txt
+++ b/tools/perf/Documentation/perf-diff.txt
@@ -95,6 +95,11 @@ OPTIONS
diff.compute config option. See COMPARISON METHODS section for
more info.

+--cycles-hist::
+ Report a histogram and the standard deviation for cycles data.
+ It can help us to judge if the reported cycles data is noisy or
+ not. This option should be used with '-c cycles'.
+
-p::
--period::
Show period values for both compared hist entries.
diff --git a/tools/perf/builtin-diff.c b/tools/perf/builtin-diff.c
index e91c0d798181..ad3f867c0429 100644
--- a/tools/perf/builtin-diff.c
+++ b/tools/perf/builtin-diff.c
@@ -21,6 +21,7 @@
#include "util/time-utils.h"
#include "util/annotate.h"
#include "util/map.h"
+#include "util/spark.h"
#include <linux/zalloc.h>

#include <errno.h>
@@ -48,6 +49,7 @@ enum {
PERF_HPP_DIFF__FORMULA,
PERF_HPP_DIFF__DELTA_ABS,
PERF_HPP_DIFF__CYCLES,
+ PERF_HPP_DIFF__CYCLES_HIST,

PERF_HPP_DIFF__MAX_INDEX
};
@@ -82,6 +84,7 @@ static bool force;
static bool show_period;
static bool show_formula;
static bool show_baseline_only;
+static bool cycles_hist;
static unsigned int sort_compute = 1;

static s64 compute_wdiff_w1;
@@ -159,6 +162,10 @@ static struct header_column {
[PERF_HPP_DIFF__CYCLES] = {
.name = "[Program Block Range] Cycles Diff",
.width = 70,
+ },
+ [PERF_HPP_DIFF__CYCLES_HIST] = {
+ .name = "stddev/Hist",
+ .width = NUM_SPARKS + 9,
}
};

@@ -605,6 +612,9 @@ static void init_block_info(struct block_info *bi, struct symbol *sym,
bi->cycles_aggr = ch->cycles_aggr;
bi->num = ch->num;
bi->num_aggr = ch->num_aggr;
+
+ memcpy(bi->cycles_spark, ch->cycles_spark,
+ NUM_SPARKS * sizeof(u64));
}

static int process_block_per_sym(struct hist_entry *he)
@@ -684,6 +694,21 @@ static struct hist_entry *get_block_pair(struct hist_entry *he,
return NULL;
}

+static void init_spark_values(unsigned long *svals, int num)
+{
+ for (int i = 0; i < num; i++)
+ svals[i] = 0;
+}
+
+static void update_spark_value(unsigned long *svals, int num,
+ struct stats *stats, u64 val)
+{
+ int n = stats->n;
+
+ if (n < num)
+ svals[n] = val;
+}
+
static void compute_cycles_diff(struct hist_entry *he,
struct hist_entry *pair)
{
@@ -692,6 +717,26 @@ static void compute_cycles_diff(struct hist_entry *he,
pair->diff.cycles =
pair->block_info->cycles_aggr / pair->block_info->num_aggr -
he->block_info->cycles_aggr / he->block_info->num_aggr;
+
+ if (!cycles_hist)
+ return;
+
+ init_stats(&pair->diff.stats);
+ init_spark_values(pair->diff.svals, NUM_SPARKS);
+
+ for (int i = 0; i < pair->block_info->num; i++) {
+ u64 val;
+
+ if (i >= he->block_info->num || i >= NUM_SPARKS)
+ break;
+
+ val = labs(pair->block_info->cycles_spark[i] -
+ he->block_info->cycles_spark[i]);
+
+ update_spark_value(pair->diff.svals, NUM_SPARKS,
+ &pair->diff.stats, val);
+ update_stats(&pair->diff.stats, val);
+ }
}
}

@@ -1250,6 +1295,9 @@ static const struct option options[] = {
"Show period values."),
OPT_BOOLEAN('F', "formula", &show_formula,
"Show formula."),
+ OPT_BOOLEAN(0, "cycles-hist", &cycles_hist,
+ "Show cycles histogram and standard deviation "
+ "- WARNING: use only with -c cycles."),
OPT_BOOLEAN('D', "dump-raw-trace", &dump_trace,
"dump raw trace in ASCII"),
OPT_BOOLEAN('f', "force", &force, "don't complain, do it"),
@@ -1457,6 +1505,90 @@ static int hpp__color_cycles(struct perf_hpp_fmt *fmt,
return __hpp__color_compare(fmt, hpp, he, COMPUTE_CYCLES);
}

+static int all_zero(unsigned long *vals, int len)
+{
+ int i;
+
+ for (i = 0; i < len; i++)
+ if (vals[i] != 0)
+ return 0;
+ return 1;
+}
+
+static int print_cycles_spark(char *bf, int size, unsigned long *svals, u64 n)
+{
+ int printed;
+
+ if (n <= 1)
+ return 0;
+
+ if (n > NUM_SPARKS)
+ n = NUM_SPARKS;
+ if (all_zero(svals, n))
+ return 0;
+
+ printed = print_spark(bf, size, svals, n);
+ printed += scnprintf(bf + printed, size - printed, " ");
+ return printed;
+}
+
+static int hpp__color_cycles_hist(struct perf_hpp_fmt *fmt,
+ struct perf_hpp *hpp, struct hist_entry *he)
+{
+ struct diff_hpp_fmt *dfmt =
+ container_of(fmt, struct diff_hpp_fmt, fmt);
+ struct hist_entry *pair = get_pair_fmt(he, dfmt);
+ struct block_hist *bh = container_of(he, struct block_hist, he);
+ struct block_hist *bh_pair;
+ struct hist_entry *block_he;
+ char spark[32], buf[128];
+ double r;
+ int ret, pad;
+
+ if (!pair) {
+ if (bh->block_idx)
+ hpp->skip = true;
+
+ goto no_print;
+ }
+
+ bh_pair = container_of(pair, struct block_hist, he);
+
+ block_he = hists__get_entry(&bh_pair->block_hists, bh->block_idx);
+ if (!block_he) {
+ hpp->skip = true;
+ goto no_print;
+ }
+
+ ret = print_cycles_spark(spark, sizeof(spark), block_he->diff.svals,
+ block_he->diff.stats.n);
+
+ r = rel_stddev_stats(stddev_stats(&block_he->diff.stats),
+ avg_stats(&block_he->diff.stats));
+
+ if (ret) {
+ /*
+ * Padding spaces if number of sparks less than NUM_SPARKS
+ * otherwise the output is not aligned.
+ */
+ pad = NUM_SPARKS - ((ret - 1) / 3);
+ scnprintf(buf, sizeof(buf), "%s%5.1f%% %s", "\u00B1", r, spark);
+ ret = scnprintf(hpp->buf, hpp->size, "%*s",
+ dfmt->header_width, buf);
+
+ if (pad) {
+ ret += scnprintf(hpp->buf + ret, hpp->size - ret,
+ "%-*s", pad, " ");
+ }
+
+ return ret;
+ }
+
+no_print:
+ return scnprintf(hpp->buf, hpp->size, "%*s",
+ dfmt->header_width, " ");
+}
+
static void
hpp__entry_unpair(struct hist_entry *he, int idx, char *buf, size_t size)
{
@@ -1662,6 +1794,10 @@ static void data__hpp_register(struct data__file *d, int idx)
fmt->color = hpp__color_cycles;
fmt->sort = hist_entry__cmp_nop;
break;
+ case PERF_HPP_DIFF__CYCLES_HIST:
+ fmt->color = hpp__color_cycles_hist;
+ fmt->sort = hist_entry__cmp_nop;
+ break;
default:
fmt->sort = hist_entry__cmp_nop;
break;
@@ -1687,10 +1823,14 @@ static int ui_init(void)
* PERF_HPP_DIFF__DELTA
* PERF_HPP_DIFF__RATIO
* PERF_HPP_DIFF__WEIGHTED_DIFF
+ * PERF_HPP_DIFF__CYCLES
*/
data__hpp_register(d, i ? compute_2_hpp[compute] :
PERF_HPP_DIFF__BASELINE);

+ if (cycles_hist && i)
+ data__hpp_register(d, PERF_HPP_DIFF__CYCLES_HIST);
+
/*
* And the rest:
*
@@ -1845,6 +1985,9 @@ int cmd_diff(int argc, const char **argv)
if (quiet)
perf_quiet_option();

+ if (cycles_hist && (compute != COMPUTE_CYCLES))
+ usage_with_options(diff_usage, options);
+
symbol__annotation_init();

if (symbol__init(NULL) < 0)
diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index 7cda749059a9..2e3ed877a703 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -89,6 +89,7 @@ perf-y += cloexec.o
perf-y += call-path.o
perf-y += rwsem.o
perf-y += thread-stack.o
+perf-y += spark.o
perf-$(CONFIG_AUXTRACE) += auxtrace.o
perf-$(CONFIG_AUXTRACE) += intel-pt-decoder/
perf-$(CONFIG_AUXTRACE) += intel-pt.o
diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
index e0518dc4c4d2..a43354dbc836 100644
--- a/tools/perf/util/annotate.c
+++ b/tools/perf/util/annotate.c
@@ -847,6 +847,10 @@ static int __symbol__account_cycles(struct cyc_hist *ch,
ch[offset].start < start)
return 0;
}
+
+ if (ch[offset].num < NUM_SPARKS)
+ ch[offset].cycles_spark[ch[offset].num] = cycles;
+
ch[offset].have_start = have_start;
ch[offset].start = start;
ch[offset].cycles += cycles;
diff --git a/tools/perf/util/annotate.h b/tools/perf/util/annotate.h
index d94be9140e31..7776ff4480af 100644
--- a/tools/perf/util/annotate.h
+++ b/tools/perf/util/annotate.h
@@ -11,6 +11,7 @@
#include <pthread.h>
#include <asm/bug.h>
#include "symbol_conf.h"
+#include "spark.h"

struct hist_browser_timer;
struct hist_entry;
@@ -235,6 +236,7 @@ struct cyc_hist {
u64 cycles_aggr;
u64 cycles_max;
u64 cycles_min;
+ s64 cycles_spark[NUM_SPARKS];
u32 num;
u32 num_aggr;
u8 have_start;
diff --git a/tools/perf/util/sort.h b/tools/perf/util/sort.h
index 5e34676a98e8..14061e42a862 100644
--- a/tools/perf/util/sort.h
+++ b/tools/perf/util/sort.h
@@ -23,6 +23,8 @@
#include "parse-events.h"
#include "hist.h"
#include "srcline.h"
+#include "stat.h"
+#include "spark.h"

struct thread;

@@ -83,6 +85,8 @@ struct hist_entry_diff {
/* PERF_HPP_DIFF__CYCLES */
s64 cycles;
};
+ struct stats stats;
+ unsigned long svals[NUM_SPARKS];
};

struct hist_entry_ops {
diff --git a/tools/perf/util/spark.c b/tools/perf/util/spark.c
new file mode 100644
index 000000000000..70272a8b81a6
--- /dev/null
+++ b/tools/perf/util/spark.c
@@ -0,0 +1,34 @@
+#include <stdio.h>
+#include <limits.h>
+#include <string.h>
+#include <stdlib.h>
+#include "spark.h"
+#include "stat.h"
+
+#define SPARK_SHIFT 8
+
+/* Print spark lines on outf for numval values in val. */
+int print_spark(char *bf, int size, unsigned long *val, int numval)
+{
+ static const char *ticks[NUM_SPARKS] = {
+ "â", "â", "â", "â", "â", "â", "â", "â"
+ };
+ int i, printed = 0;
+ unsigned long min = ULONG_MAX, max = 0, f;
+
+ 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++) {
+ printed += scnprintf(bf + printed, size - printed, "%s",
+ ticks[((val[i] - min) << SPARK_SHIFT) / f]);
+ }
+
+ return printed;
+}
diff --git a/tools/perf/util/spark.h b/tools/perf/util/spark.h
new file mode 100644
index 000000000000..25402d7d7a64
--- /dev/null
+++ b/tools/perf/util/spark.h
@@ -0,0 +1,8 @@
+#ifndef SPARK_H
+#define SPARK_H 1
+
+#define NUM_SPARKS 8
+
+int print_spark(char *bf, int size, unsigned long *val, int numval);
+
+#endif
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index 183f630cb5f1..499917165394 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -12,6 +12,7 @@
#include "branch.h"
#include "path.h"
#include "symbol_conf.h"
+#include "spark.h"

#ifdef HAVE_LIBELF_SUPPORT
#include <libelf.h>
@@ -137,6 +138,7 @@ struct block_info {
u64 end;
u64 cycles;
u64 cycles_aggr;
+ s64 cycles_spark[NUM_SPARKS];
int num;
int num_aggr;
refcount_t refcnt;
--
2.17.1