On Tue, May 18, 2021 at 11:55 AM Suren Baghdasaryan [off-list ref] wrote:

On Tue, May 18, 2021 at 11:52 AM Peter Zijlstra [off-list ref] wrote:

quoted

On Mon, May 17, 2021 at 07:02:00PM -0700, Suren Baghdasaryan wrote:

quoted

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index cc25a3cff41f..4b8e72640ac9 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c

@@ -148,6 +148,7 @@
 static int psi_bug __read_mostly;

 DEFINE_STATIC_KEY_FALSE(psi_disabled);
+DEFINE_STATIC_KEY_FALSE(psi_cgroups_disabled);

I'm thinking the whole thing will be easier/clearer when you make this:

DEFINE_STATIC_KEY_TRUE(psi_cgroups_enabled);

Sounds good. Will respin another version. Thanks for reviewing!

v3 is posted at https://lore.kernel.org/patchwork/patch/1435705

quoted

quoted

 #ifdef CONFIG_PSI_DEFAULT_DISABLED
 static bool psi_enable;

@@ -211,6 +212,9 @@ void __init psi_init(void)
              return;
      }

+     if (!cgroup_psi_enabled())
+             static_branch_enable(&psi_cgroups_disabled);

        if (!cgroup_psi_enabled())
                static_branch_disable(&psi_cgroups_enabled);

quoted

+
      psi_period = jiffies_to_nsecs(PSI_FREQ);
      group_init(&psi_system);
 }

@@ -744,23 +748,23 @@ static void psi_group_change(struct psi_group *group, int cpu,

 static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
 {
+     if (*iter == &psi_system)
+             return NULL;
+
 #ifdef CONFIG_CGROUPS
+     if (!static_branch_likely(&psi_cgroups_disabled)) {

        if (static_branch_likely(&psi_cgroups_enabled)) {

quoted

+             struct cgroup *cgroup = NULL;

+             if (!*iter)
+                     cgroup = task->cgroups->dfl_cgrp;
+             else
+                     cgroup = cgroup_parent(*iter);

+             if (cgroup && cgroup_parent(cgroup)) {
+                     *iter = cgroup;
+                     return cgroup_psi(cgroup);
+             }
      }
 #endif
      *iter = &psi_system;
      return &psi_system;

But yes, very nice.

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