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report-basic: add idle/iowait/steal as CPUWait family

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As discussed in the PR, those fields can go down, so they cannot be advertised
as type COUNTER. But the type is shared for the whole family, so we need to
create a new family to keep the other ones as COUNTER and add the new ones
as GAUGE.

kernel/sched/cputime.c says above get_cpu_idle_time_us() and get_cpu_iowait_time_us():
> Note that this is partially broken due to the counter of iowait tasks that
> can be remotely updated without any synchronization. Therefore it is possible
> to observe backward values within two consecutive reads.

steal is apparently also unreliable because it is reported by the hyperviser.
So let's be cautious and report it as gauge too.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
2026-08-24 23:56:06 +02:00
parent b8cc2ef04b
commit 65ba2ff4a7
2 changed files with 43 additions and 10 deletions
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src/report/report-basic.c
+30 -9
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@@ -237,10 +237,11 @@ static int cpus_online_generate(const MetricFamily *mf, sd_varlink *link, void *
/* fields= */ NULL);
}
static int cpu_usage_generate(const MetricFamily *mf, sd_varlink *link, void *userdata) {
static int cpu_usage_generate(const MetricFamily mf[static 2], sd_varlink *link, void *userdata) {
int r;
assert(mf && mf->name);
assert(mf && mf[0].name && mf[1].name);
assert(!mf[1].generate);
assert(link);
/* The aggregate "cpu" line of /proc/stat, converted from USER_HZ ticks to nanoseconds, matching
@@ -254,24 +255,36 @@ static int cpu_usage_generate(const MetricFamily *mf, sd_varlink *link, void *us
return 0;
}
static const char* const types[] = { "user", "system" };
const uint64_t values[] = {
static const struct {
const char *name;
size_t family_offset;
} attributes[] = {
{ "user", 0 },
{ "system", 0 },
{ "idle", 1 },
{ "iowait", 1 },
{ "steal", 1 },
};
uint64_t values[] = {
ticks.user + ticks.nice,
ticks.system + ticks.irq + ticks.softirq,
ticks.idle,
ticks.iowait,
ticks.steal,
};
assert_cc(ELEMENTSOF(types) == ELEMENTSOF(values));
assert_cc(ELEMENTSOF(attributes) == ELEMENTSOF(values));
for (size_t i = 0; i < ELEMENTSOF(values); i++) {
for (size_t i = 0; i < ELEMENTSOF(attributes); i++) {
_cleanup_(sd_json_variant_unrefp) sd_json_variant *fields = NULL;
r = sd_json_buildo(&fields, SD_JSON_BUILD_PAIR_STRING("type", types[i]));
r = sd_json_buildo(&fields, SD_JSON_BUILD_PAIR_STRING("type", attributes[i].name));
if (r < 0)
return r;
uint64_t nsec = procfs_ticks_to_nsec(values[i]);
r = metric_build_send_unsigned(
mf,
&mf[attributes[i].family_offset],
link,
/* object= */ NULL,
nsec,
@@ -719,7 +732,7 @@ static int virtualization_generate(const MetricFamily *mf, sd_varlink *link, voi
}
static const MetricFamily metric_family_table[] = {
/* Keep entries ordered alphabetically */
/* Keep entries (with .generate) ordered alphabetically */
{
METRIC_IO_SYSTEMD_BASIC_PREFIX "Architecture",
"CPU architecture",
@@ -744,12 +757,20 @@ static const MetricFamily metric_family_table[] = {
METRIC_FAMILY_TYPE_GAUGE,
.generate = cpus_online_generate,
},
/* METRIC_FAMILY_TYPE_COUNTER must be monotonic, but steal and iowait can go down,
* so CPUUsage is split into two families of different types. */
{
METRIC_IO_SYSTEMD_BASIC_PREFIX "CPUUsage",
"Aggregate CPU usage across all CPUs in nanoseconds (type=user|system)",
METRIC_FAMILY_TYPE_COUNTER,
.generate = cpu_usage_generate,
},
{
METRIC_IO_SYSTEMD_BASIC_PREFIX "CPUWait",
"Aggregate CPU wait across all CPUs in nanoseconds (type=idle|iowait|steal)",
METRIC_FAMILY_TYPE_GAUGE,
},
/* Keep those ↑ in sync with cpu_usage_generate(). */
{
METRIC_IO_SYSTEMD_BASIC_PREFIX "DiskReadBytes",
"Per block device metric: cumulative number of bytes read "