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psi: Fix cpu.pressure for cpu.max and competing cgroups

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For simplicity, cpu pressure is defined as having more than one
runnable task on a given CPU. This works on the system-level, but it
has limitations in a cgrouped reality: When cpu.max is in use, it
doesn't capture the time in which a task is not executing on the CPU
due to throttling. Likewise, it doesn't capture the time in which a
competing cgroup is occupying the CPU - meaning it only reflects
cgroup-internal competitive pressure, not outside pressure.

Enable tracking of currently executing tasks, and then change the
definition of cpu pressure in a cgroup from

	NR_RUNNING > 1

to

	NR_RUNNING > ON_CPU

which will capture the effects of cpu.max as well as competition from
outside the cgroup.

After this patch, a cgroup running `stress -c 1` with a cpu.max
setting of 5000 10000 shows ~50% continuous CPU pressure.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200316191333.115523-2-hannes@cmpxchg.org
This commit is contained in:
Johannes Weiner
2020-03-16 15:13:31 -04:00
committed by Peter Zijlstra
parent 46a87b3851
commit b05e75d611
4 changed files with 46 additions and 6 deletions
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12
kernel/sched/psi.c
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@@ -225,7 +225,7 @@ 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] > 1;
return tasks[NR_RUNNING] > tasks[NR_ONCPU];
case PSI_NONIDLE:
return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] ||
tasks[NR_RUNNING];
@@ -695,10 +695,10 @@ static u32 psi_group_change(struct psi_group *group, int cpu,
if (!(m & (1 << t)))
continue;
if (groupc->tasks[t] == 0 && !psi_bug) {
printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u] clear=%x set=%x\n",
printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u %u] clear=%x set=%x\n",
cpu, t, groupc->tasks[0],
groupc->tasks[1], groupc->tasks[2],
clear, set);
groupc->tasks[3], clear, set);
psi_bug = 1;
}
groupc->tasks[t]--;
@@ -916,9 +916,11 @@ void cgroup_move_task(struct task_struct *task, struct css_set *to)
rq = task_rq_lock(task, &rf);
if (task_on_rq_queued(task))
if (task_on_rq_queued(task)) {
task_flags = TSK_RUNNING;
else if (task->in_iowait)
if (task_current(rq, task))
task_flags |= TSK_ONCPU;
} else if (task->in_iowait)
task_flags = TSK_IOWAIT;
if (task->flags & PF_MEMSTALL)