[PATCH] psi: Add PSI_CPU_FULL state

[PATCH] psi: Add PSI_CPU_FULL state

[Chengming Zhou]

From: zhouchengming <zhouchengming@bytedance.com>

When I run a simple "perf bench sched pipe" test in a cgroup on my
machine, the output of "watch -d -n 1 cpu.pressure" of this cgroup
will report some avg10 10%-20%.
It's strange because there is not any other process in the cgroup.
Then I found that cpu contention/wait percentage came from outside
of the cgroup and the cpu idle latency, not wait for threads in
the cgroup.
So I think adding PSI_CPU_FULL state will be useful for container
workloads to distinguish between outside cgroup resource contention
and inside cgroup resource contention.
What's more, the PSI_CPU_FULL state includes the latency of the cpu
idle itself, so we can see the system sum latency introduced by cpu
idle state.

Signed-off-by: zhouchengming <zhouchengming@bytedance.com>
---
 include/linux/psi_types.h | 3 ++-
 kernel/sched/psi.c        | 9 +++++++--
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
index b95f3211566a..0a23300d49af 100644
--- a/include/linux/psi_types.h
+++ b/include/linux/psi_types.h
@@ -50,9 +50,10 @@ enum psi_states {
 	PSI_MEM_SOME,
 	PSI_MEM_FULL,
 	PSI_CPU_SOME,
+	PSI_CPU_FULL,
 	/* Only per-CPU, to weigh the CPU in the global average: */
 	PSI_NONIDLE,
-	NR_PSI_STATES = 6,
+	NR_PSI_STATES = 7,
 };
 
 enum psi_aggregators {
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 967732c0766c..234047e368a5 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -224,7 +224,9 @@ static bool test_state(unsigned int *tasks, enum psi_states state)
 	case PSI_MEM_FULL:
 		return tasks[NR_MEMSTALL] && !tasks[NR_RUNNING];
 	case PSI_CPU_SOME:
-		return tasks[NR_RUNNING] > tasks[NR_ONCPU];
+		return tasks[NR_RUNNING] > tasks[NR_ONCPU] && tasks[NR_ONCPU];
+	case PSI_CPU_FULL:
+		return tasks[NR_RUNNING] && !tasks[NR_ONCPU];
 	case PSI_NONIDLE:
 		return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] ||
 			tasks[NR_RUNNING];
@@ -681,6 +683,9 @@ static void record_times(struct psi_group_cpu *groupc, int cpu,
 	if (groupc->state_mask & (1 << PSI_CPU_SOME))
 		groupc->times[PSI_CPU_SOME] += delta;
 
+	if (groupc->state_mask & (1 << PSI_CPU_FULL))
+		groupc->times[PSI_CPU_FULL] += delta;
+
 	if (groupc->state_mask & (1 << PSI_NONIDLE))
 		groupc->times[PSI_NONIDLE] += delta;
 }
@@ -1018,7 +1023,7 @@ int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
 		group->avg_next_update = update_averages(group, now);
 	mutex_unlock(&group->avgs_lock);
 
-	for (full = 0; full < 2 - (res == PSI_CPU); full++) {
+	for (full = 0; full < 2; full++) {
 		unsigned long avg[3];
 		u64 total;
 		int w;
-- 
2.11.0

Re: [PATCH] psi: Add PSI_CPU_FULL state

[Johannes Weiner]

On Sun, Feb 07, 2021 at 03:24:02PM +0800, Chengming Zhou wrote:
> The FULL state doesn't exist for the CPU resource at the system level,
> but exist at the cgroup level, means all non-idle tasks in a cgroup are
> delayed on the CPU resource which used by others outside of the cgroup.
> 
> Co-developed-by: Muchun Song <songmuchun@bytedance.com>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

That metric's come up in our production environment recently as well,
it makes a lot of sense.

In addition to outside competition, this also applies to downtimes
enforced by cpu.max - another cgroup usecase that is worth mentioning
in the changelog & code comment.

Thanks

[PATCH] psi: Add PSI_CPU_FULL state

[Chengming Zhou]

The FULL state doesn't exist for the CPU resource at the system level,
but exist at the cgroup level, means all non-idle tasks in a cgroup are
delayed on the CPU resource which used by others outside of the cgroup.

Co-developed-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
 include/linux/psi_types.h |  3 ++-
 kernel/sched/psi.c        | 14 +++++++++++---
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
index b95f3211566a..0a23300d49af 100644
--- a/include/linux/psi_types.h
+++ b/include/linux/psi_types.h
@@ -50,9 +50,10 @@ enum psi_states {
 	PSI_MEM_SOME,
 	PSI_MEM_FULL,
 	PSI_CPU_SOME,
+	PSI_CPU_FULL,
 	/* Only per-CPU, to weigh the CPU in the global average: */
 	PSI_NONIDLE,
-	NR_PSI_STATES = 6,
+	NR_PSI_STATES = 7,
 };
 
 enum psi_aggregators {
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 39d758a15a57..c572ad529d87 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -34,7 +34,10 @@
  * delayed on that resource such that nobody is advancing and the CPU
  * goes idle. This leaves both workload and CPU unproductive.
  *
- * (Naturally, the FULL state doesn't exist for the CPU resource.)
+ * Naturally, the FULL state doesn't exist for the CPU resource at the
+ * system level, but exist at the cgroup level, means all non-idle tasks
+ * in a cgroup are delayed on the CPU resource which used by others outside
+ * of the cgroup.
  *
  *	SOME = nr_delayed_tasks != 0
  *	FULL = nr_delayed_tasks != 0 && nr_running_tasks == 0
@@ -225,6 +228,8 @@ static bool test_state(unsigned int *tasks, enum psi_states state)
 		return tasks[NR_MEMSTALL] && !tasks[NR_RUNNING];
 	case PSI_CPU_SOME:
 		return tasks[NR_RUNNING] > tasks[NR_ONCPU];
+	case PSI_CPU_FULL:
+		return tasks[NR_RUNNING] && !tasks[NR_ONCPU];
 	case PSI_NONIDLE:
 		return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] ||
 			tasks[NR_RUNNING];
@@ -678,8 +683,11 @@ static void record_times(struct psi_group_cpu *groupc, int cpu,
 		}
 	}
 
-	if (groupc->state_mask & (1 << PSI_CPU_SOME))
+	if (groupc->state_mask & (1 << PSI_CPU_SOME)) {
 		groupc->times[PSI_CPU_SOME] += delta;
+		if (groupc->state_mask & (1 << PSI_CPU_FULL))
+			groupc->times[PSI_CPU_FULL] += delta;
+	}
 
 	if (groupc->state_mask & (1 << PSI_NONIDLE))
 		groupc->times[PSI_NONIDLE] += delta;
@@ -1018,7 +1026,7 @@ int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
 		group->avg_next_update = update_averages(group, now);
 	mutex_unlock(&group->avgs_lock);
 
-	for (full = 0; full < 2 - (res == PSI_CPU); full++) {
+	for (full = 0; full < 2; full++) {
 		unsigned long avg[3];
 		u64 total;
 		int w;
-- 
2.11.0