[RFC 1/3] perf tools: Fix weight sort key behavior
From: Namhyung Kim
Date: Fri Nov 05 2021 - 18:56:29 EST
Currently, the weight field in the perf sample has latency information
for some instructions like in memory access. And perf tool has weight
and local_weight sort keys to display the info.
But it's somewhat confusing what it shows exactly. In my understanding,
the local_weight shows a weight in a single sample, and (global) weight
shows a sum of the weights in the hist_entry.
For example,
$ perf mem record -t load dd if=/dev/zero of=/dev/null bs=4k count=1M
$ perf report --stdio -n -s +local_weight
...
#
# Overhead Samples Command Shared Object Symbol Local Weight
# ........ ............ ....... ................ ................................... ............
#
21.23% 313 dd [kernel.vmlinux] [k] lockref_get_not_zero 32
12.43% 183 dd [kernel.vmlinux] [k] lockref_get_not_zero 35
11.97% 159 dd [kernel.vmlinux] [k] lockref_get_not_zero 36
10.40% 141 dd [kernel.vmlinux] [k] lockref_put_return 32
7.63% 113 dd [kernel.vmlinux] [k] lockref_get_not_zero 33
6.37% 92 dd [kernel.vmlinux] [k] lockref_get_not_zero 34
6.15% 90 dd [kernel.vmlinux] [k] lockref_put_return 33
...
So let's look at the lockref_get_not_zero symbols. The top entry shows
that 313 samples were captured with local_weight 32, so the total weight
should be 313 x 32 = 10016. But it's not the case like below:
$ perf report --stdio -n -s +local_weight,weight -S lockref_get_not_zero
...
#
# Overhead Samples Command Shared Object Local Weight Weight
# ........ ............ ....... ................ ............ ............
#
1.36% 4 dd [kernel.vmlinux] 36 144
0.47% 4 dd [kernel.vmlinux] 37 148
0.42% 4 dd [kernel.vmlinux] 32 128
0.40% 4 dd [kernel.vmlinux] 34 136
0.35% 4 dd [kernel.vmlinux] 36 144
0.34% 4 dd [kernel.vmlinux] 35 140
0.30% 4 dd [kernel.vmlinux] 36 144
0.30% 4 dd [kernel.vmlinux] 34 136
0.30% 4 dd [kernel.vmlinux] 32 128
0.30% 4 dd [kernel.vmlinux] 32 128
...
With 'weight' sort key, it's divided to 4 samples even with same info
(comm,dso,sym and local_weight). I don't think this is what we want.
I found this is because of the way it aggregate the weight value.
Since it's not a period, we should not add them in the he->stat.
Otherwise, two 32 weight entries will create a 64 weight entry.
After that, new 32 weight samples don't have a matching entry so it'd
create a new entry and make it a 64 weight entry again and again.
Later, they will be merged into 128 weight entries during the
hists__collapse_resort() with 4 samples, multiple times like above.
Let's keep the weight and display differently. For local_weight, it
can show the weight as is, and for (global) weight it can display the
number multiplied by the number of samples.
With this change, I can see the expected numbers.
$ perf report --stdio -n -s +local_weight,weight -S lockref_get_not_zero
...
#
# Overhead Samples Command Shared Object Local Weight Weight
# ........ ............ ....... ................ ............ ............
#
21.23% 313 dd [kernel.vmlinux] 32 10016
12.43% 183 dd [kernel.vmlinux] 35 6405
11.97% 159 dd [kernel.vmlinux] 36 5724
7.63% 113 dd [kernel.vmlinux] 33 3729
6.37% 92 dd [kernel.vmlinux] 34 3128
4.17% 59 dd [kernel.vmlinux] 37 2183
0.08% 1 dd [kernel.vmlinux] 269 269
0.08% 1 dd [kernel.vmlinux] 38 38
Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Cc: Athira Rajeev <atrajeev@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
tools/perf/util/hist.c | 14 +++++---------
tools/perf/util/sort.c | 24 +++++++-----------------
tools/perf/util/sort.h | 2 +-
3 files changed, 13 insertions(+), 27 deletions(-)
diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
index 65fe65ba03c2..4e9bd7b589b1 100644
--- a/tools/perf/util/hist.c
+++ b/tools/perf/util/hist.c
@@ -290,11 +290,9 @@ static long hist_time(unsigned long htime)
}
static void he_stat__add_period(struct he_stat *he_stat, u64 period,
- u64 weight, u64 ins_lat, u64 p_stage_cyc)
+ u64 ins_lat, u64 p_stage_cyc)
{
-
he_stat->period += period;
- he_stat->weight += weight;
he_stat->nr_events += 1;
he_stat->ins_lat += ins_lat;
he_stat->p_stage_cyc += p_stage_cyc;
@@ -308,9 +306,8 @@ static void he_stat__add_stat(struct he_stat *dest, struct he_stat *src)
dest->period_guest_sys += src->period_guest_sys;
dest->period_guest_us += src->period_guest_us;
dest->nr_events += src->nr_events;
- dest->weight += src->weight;
dest->ins_lat += src->ins_lat;
- dest->p_stage_cyc += src->p_stage_cyc;
+ dest->p_stage_cyc += src->p_stage_cyc;
}
static void he_stat__decay(struct he_stat *he_stat)
@@ -598,7 +595,6 @@ static struct hist_entry *hists__findnew_entry(struct hists *hists,
struct hist_entry *he;
int64_t cmp;
u64 period = entry->stat.period;
- u64 weight = entry->stat.weight;
u64 ins_lat = entry->stat.ins_lat;
u64 p_stage_cyc = entry->stat.p_stage_cyc;
bool leftmost = true;
@@ -619,11 +615,11 @@ static struct hist_entry *hists__findnew_entry(struct hists *hists,
if (!cmp) {
if (sample_self) {
- he_stat__add_period(&he->stat, period, weight, ins_lat, p_stage_cyc);
+ he_stat__add_period(&he->stat, period, ins_lat, p_stage_cyc);
hist_entry__add_callchain_period(he, period);
}
if (symbol_conf.cumulate_callchain)
- he_stat__add_period(he->stat_acc, period, weight, ins_lat, p_stage_cyc);
+ he_stat__add_period(he->stat_acc, period, ins_lat, p_stage_cyc);
/*
* This mem info was allocated from sample__resolve_mem
@@ -733,7 +729,6 @@ __hists__add_entry(struct hists *hists,
.stat = {
.nr_events = 1,
.period = sample->period,
- .weight = sample->weight,
.ins_lat = sample->ins_lat,
.p_stage_cyc = sample->p_stage_cyc,
},
@@ -748,6 +743,7 @@ __hists__add_entry(struct hists *hists,
.raw_size = sample->raw_size,
.ops = ops,
.time = hist_time(sample->time),
+ .weight = sample->weight,
}, *he = hists__findnew_entry(hists, &entry, al, sample_self);
if (!hists->has_callchains && he && he->callchain_size != 0)
diff --git a/tools/perf/util/sort.c b/tools/perf/util/sort.c
index 568a88c001c6..903f34fff27e 100644
--- a/tools/perf/util/sort.c
+++ b/tools/perf/util/sort.c
@@ -1325,45 +1325,35 @@ struct sort_entry sort_mispredict = {
.se_width_idx = HISTC_MISPREDICT,
};
-static u64 he_weight(struct hist_entry *he)
-{
- return he->stat.nr_events ? he->stat.weight / he->stat.nr_events : 0;
-}
-
static int64_t
-sort__local_weight_cmp(struct hist_entry *left, struct hist_entry *right)
+sort__weight_cmp(struct hist_entry *left, struct hist_entry *right)
{
- return he_weight(left) - he_weight(right);
+ return left->weight - right->weight;
}
static int hist_entry__local_weight_snprintf(struct hist_entry *he, char *bf,
size_t size, unsigned int width)
{
- return repsep_snprintf(bf, size, "%-*llu", width, he_weight(he));
+ return repsep_snprintf(bf, size, "%-*llu", width, he->weight);
}
struct sort_entry sort_local_weight = {
.se_header = "Local Weight",
- .se_cmp = sort__local_weight_cmp,
+ .se_cmp = sort__weight_cmp,
.se_snprintf = hist_entry__local_weight_snprintf,
.se_width_idx = HISTC_LOCAL_WEIGHT,
};
-static int64_t
-sort__global_weight_cmp(struct hist_entry *left, struct hist_entry *right)
-{
- return left->stat.weight - right->stat.weight;
-}
-
static int hist_entry__global_weight_snprintf(struct hist_entry *he, char *bf,
size_t size, unsigned int width)
{
- return repsep_snprintf(bf, size, "%-*llu", width, he->stat.weight);
+ return repsep_snprintf(bf, size, "%-*llu", width,
+ he->weight * he->stat.nr_events);
}
struct sort_entry sort_global_weight = {
.se_header = "Weight",
- .se_cmp = sort__global_weight_cmp,
+ .se_cmp = sort__weight_cmp,
.se_snprintf = hist_entry__global_weight_snprintf,
.se_width_idx = HISTC_GLOBAL_WEIGHT,
};
diff --git a/tools/perf/util/sort.h b/tools/perf/util/sort.h
index b67c469aba79..e18b79916f63 100644
--- a/tools/perf/util/sort.h
+++ b/tools/perf/util/sort.h
@@ -49,7 +49,6 @@ struct he_stat {
u64 period_us;
u64 period_guest_sys;
u64 period_guest_us;
- u64 weight;
u64 ins_lat;
u64 p_stage_cyc;
u32 nr_events;
@@ -109,6 +108,7 @@ struct hist_entry {
s32 socket;
s32 cpu;
u64 code_page_size;
+ u64 weight;
u8 cpumode;
u8 depth;
--
2.34.0.rc0.344.g81b53c2807-goog