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Subject[RFC PATCH 12/14] sched: Implement interface for cgroup unified hierarchy
Date
From: Tejun Heo <tj@kernel.org>

While the cpu controller doesn't have any functional problems, there
are a couple interface issues which can be addressed in the v2
interface.

* cpuacct being a separate controller. This separation is artificial
and rather pointless as demonstrated by most use cases co-mounting
the two controllers. It also forces certain information to be
accounted twice.

* Use of different time units. Writable control knobs use
microseconds, some stat fields use nanoseconds while other cpuacct
stat fields use centiseconds.

* Control knobs which can't be used in the root cgroup still show up
in the root.

* Control knob names and semantics aren't consistent with other
controllers.

This patchset implements cpu controller's interface on the unified
hierarchy which adheres to the controller file conventions described in
Documentation/cgroup-v2.txt. Overall, the following changes are made.

* cpuacct is implictly enabled and disabled by cpu and its information
is reported through "cpu.stat" which now uses microseconds for all
time durations. All time duration fields now have "_usec" appended
to them for clarity. While this doesn't solve the double accounting
immediately, once majority of users switch to v2, cpu can directly
account and report the relevant stats and cpuacct can be disabled on
the unified hierarchy.

Note that cpuacct.usage_percpu is currently not included in
"cpu.stat". If this information is actually called for, it can be
added later.

* "cpu.shares" is replaced with "cpu.weight" and operates on the
standard scale defined by CGROUP_WEIGHT_MIN/DFL/MAX (1, 100, 10000).
The weight is scaled to scheduler weight so that 100 maps to 1024
and the ratio relationship is preserved - if weight is W and its
scaled value is S, W / 100 == S / 1024. While the mapped range is a
bit smaller than the orignal scheduler weight range, the dead zones
on both sides are relatively small and covers wider range than the
nice value mappings. This file doesn't make sense in the root
cgroup and isn't create on root.

* "cpu.cfs_quota_us" and "cpu.cfs_period_us" are replaced by "cpu.max"
which contains both quota and period.

* "cpu.rt_runtime_us" and "cpu.rt_period_us" are replaced by
"cpu.rt.max" which contains both runtime and period.

v2: cpu_stats_show() was incorrectly using CONFIG_FAIR_GROUP_SCHED for
CFS bandwidth stats and also using raw division for u64. Use
CONFIG_CFS_BANDWITH and do_div() instead.

The semantics of "cpu.rt.max" is not fully decided yet. Dropped
for now.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
---
kernel/sched/core.c | 141 +++++++++++++++++++++++++++++++++++++++++++++++++
kernel/sched/cpuacct.c | 25 +++++++++
kernel/sched/cpuacct.h | 5 ++
3 files changed, 171 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5e3a217..78dfcaa 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7288,6 +7288,139 @@ static u64 cpu_rt_period_read_uint(struct cgroup_subsys_state *css,
{ } /* Terminate */
};

+static int cpu_stats_show(struct seq_file *sf, void *v)
+{
+ cpuacct_cpu_stats_show(sf);
+
+#ifdef CONFIG_CFS_BANDWIDTH
+ {
+ struct task_group *tg = css_tg(seq_css(sf));
+ struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
+ u64 throttled_usec;
+
+ throttled_usec = cfs_b->throttled_time;
+ do_div(throttled_usec, NSEC_PER_USEC);
+
+ seq_printf(sf, "nr_periods %d\n"
+ "nr_throttled %d\n"
+ "throttled_usec %llu\n",
+ cfs_b->nr_periods, cfs_b->nr_throttled,
+ throttled_usec);
+ }
+#endif
+ return 0;
+}
+
+#ifdef CONFIG_FAIR_GROUP_SCHED
+static u64 cpu_weight_read_u64(struct cgroup_subsys_state *css,
+ struct cftype *cft)
+{
+ struct task_group *tg = css_tg(css);
+ u64 weight = scale_load_down(tg->shares);
+
+ return DIV_ROUND_CLOSEST_ULL(weight * CGROUP_WEIGHT_DFL, 1024);
+}
+
+static int cpu_weight_write_u64(struct cgroup_subsys_state *css,
+ struct cftype *cftype, u64 weight)
+{
+ /*
+ * cgroup weight knobs should use the common MIN, DFL and MAX
+ * values which are 1, 100 and 10000 respectively. While it loses
+ * a bit of range on both ends, it maps pretty well onto the shares
+ * value used by scheduler and the round-trip conversions preserve
+ * the original value over the entire range.
+ */
+ if (weight < CGROUP_WEIGHT_MIN || weight > CGROUP_WEIGHT_MAX)
+ return -ERANGE;
+
+ weight = DIV_ROUND_CLOSEST_ULL(weight * 1024, CGROUP_WEIGHT_DFL);
+
+ return sched_group_set_shares(css_tg(css), scale_load(weight));
+}
+#endif
+
+static void __maybe_unused cpu_period_quota_print(struct seq_file *sf,
+ long period, long quota)
+{
+ if (quota < 0)
+ seq_puts(sf, "max");
+ else
+ seq_printf(sf, "%ld", quota);
+
+ seq_printf(sf, " %ld\n", period);
+}
+
+/* caller should put the current value in *@periodp before calling */
+static int __maybe_unused cpu_period_quota_parse(char *buf,
+ u64 *periodp, u64 *quotap)
+{
+ char tok[21]; /* U64_MAX */
+
+ if (!sscanf(buf, "%s %llu", tok, periodp))
+ return -EINVAL;
+
+ *periodp *= NSEC_PER_USEC;
+
+ if (sscanf(tok, "%llu", quotap))
+ *quotap *= NSEC_PER_USEC;
+ else if (!strcmp(tok, "max"))
+ *quotap = RUNTIME_INF;
+ else
+ return -EINVAL;
+
+ return 0;
+}
+
+#ifdef CONFIG_CFS_BANDWIDTH
+static int cpu_max_show(struct seq_file *sf, void *v)
+{
+ struct task_group *tg = css_tg(seq_css(sf));
+
+ cpu_period_quota_print(sf, tg_get_cfs_period(tg), tg_get_cfs_quota(tg));
+ return 0;
+}
+
+static ssize_t cpu_max_write(struct kernfs_open_file *of,
+ char *buf, size_t nbytes, loff_t off)
+{
+ struct task_group *tg = css_tg(of_css(of));
+ u64 period = tg_get_cfs_period(tg);
+ u64 quota;
+ int ret;
+
+ ret = cpu_period_quota_parse(buf, &period, &quota);
+ if (!ret)
+ ret = tg_set_cfs_bandwidth(tg, period, quota);
+ return ret ?: nbytes;
+}
+#endif
+
+static struct cftype cpu_files[] = {
+ {
+ .name = "stat",
+ .flags = CFTYPE_NOT_ON_ROOT,
+ .seq_show = cpu_stats_show,
+ },
+#ifdef CONFIG_FAIR_GROUP_SCHED
+ {
+ .name = "weight",
+ .flags = CFTYPE_NOT_ON_ROOT,
+ .read_u64 = cpu_weight_read_u64,
+ .write_u64 = cpu_weight_write_u64,
+ },
+#endif
+#ifdef CONFIG_CFS_BANDWIDTH
+ {
+ .name = "max",
+ .flags = CFTYPE_NOT_ON_ROOT,
+ .seq_show = cpu_max_show,
+ .write = cpu_max_write,
+ },
+#endif
+ { } /* terminate */
+};
+
struct cgroup_subsys cpu_cgrp_subsys = {
.css_alloc = cpu_cgroup_css_alloc,
.css_online = cpu_cgroup_css_online,
@@ -7297,7 +7430,15 @@ struct cgroup_subsys cpu_cgrp_subsys = {
.can_attach = cpu_cgroup_can_attach,
.attach = cpu_cgroup_attach,
.legacy_cftypes = cpu_legacy_files,
+ .dfl_cftypes = cpu_files,
.early_init = true,
+#ifdef CONFIG_CGROUP_CPUACCT
+ /*
+ * cpuacct is enabled together with cpu on the unified hierarchy
+ * and its stats are reported through "cpu.stat".
+ */
+ .depends_on = 1 << cpuacct_cgrp_id,
+#endif
};

#endif /* CONFIG_CGROUP_SCHED */
diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index 6151c23..fc1cf13 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -347,6 +347,31 @@ static int cpuacct_stats_show(struct seq_file *sf, void *v)
{ } /* terminate */
};

+/* used to print cpuacct stats in cpu.stat on the unified hierarchy */
+void cpuacct_cpu_stats_show(struct seq_file *sf)
+{
+ struct cgroup_subsys_state *css;
+ u64 usage, val[CPUACCT_STAT_NSTATS];
+
+ css = cgroup_get_e_css(seq_css(sf)->cgroup, &cpuacct_cgrp_subsys);
+
+ usage = cpuusage_read(css, seq_cft(sf));
+ cpuacct_stats_read(css_ca(css), &val);
+
+ val[CPUACCT_STAT_USER] *= TICK_NSEC;
+ val[CPUACCT_STAT_SYSTEM] *= TICK_NSEC;
+ do_div(usage, NSEC_PER_USEC);
+ do_div(val[CPUACCT_STAT_USER], NSEC_PER_USEC);
+ do_div(val[CPUACCT_STAT_SYSTEM], NSEC_PER_USEC);
+
+ seq_printf(sf, "usage_usec %llu\n"
+ "user_usec %llu\n"
+ "system_usec %llu\n",
+ usage, val[CPUACCT_STAT_USER], val[CPUACCT_STAT_SYSTEM]);
+
+ css_put(css);
+}
+
/*
* charge this task's execution time to its accounting group.
*
diff --git a/kernel/sched/cpuacct.h b/kernel/sched/cpuacct.h
index ba72807..ddf7af4 100644
--- a/kernel/sched/cpuacct.h
+++ b/kernel/sched/cpuacct.h
@@ -2,6 +2,7 @@

extern void cpuacct_charge(struct task_struct *tsk, u64 cputime);
extern void cpuacct_account_field(struct task_struct *tsk, int index, u64 val);
+extern void cpuacct_cpu_stats_show(struct seq_file *sf);

#else

@@ -14,4 +15,8 @@ static inline void cpuacct_charge(struct task_struct *tsk, u64 cputime)
{
}

+static inline void cpuacct_cpu_stats_show(struct seq_file *sf)
+{
+}
+
#endif
--
1.8.3.1
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