On Fri, May 14, 2021 at 11:50 AM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:
>
> On Fri, May 14, 2021 at 11:20 AM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:
> >
> > On Fri, May 14, 2021 at 10:52 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > >
> > > On Fri, May 14, 2021 at 08:54:47AM -0700, Suren Baghdasaryan wrote:
> > >
> > > > Correct, for this function CONFIG_CGROUPS=n and
> > > > cgroup_disable=pressure are treated the same. True, from the code it's
> > > > not very obvious. Do you have some refactoring in mind that would make
> > > > it more explicit?
> > >
> > > Does this make sense?
> > >
> > > --- a/kernel/sched/psi.c
> > > +++ b/kernel/sched/psi.c
> > > @@ -744,24 +744,26 @@ static void psi_group_change(struct psi_
> > >
> > > static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
> > > {
> > > + if (cgroup_psi_enabled()) {
> > > #ifdef CONFIG_CGROUPS
> > > - struct cgroup *cgroup = NULL;
> > > + struct cgroup *cgroup = NULL;
> > >
> > > - if (!*iter)
> > > - cgroup = task->cgroups->dfl_cgrp;
> > > - else if (*iter == &psi_system)
> > > - return NULL;
> > > - else
> > > - cgroup = cgroup_parent(*iter);
> > > + if (!*iter)
> > > + cgroup = task->cgroups->dfl_cgrp;
> > > + else if (*iter == &psi_system)
> > > + return NULL;
> > > + else
> > > + cgroup = cgroup_parent(*iter);
> > >
> > > - if (cgroup && cgroup_parent(cgroup)) {
> > > - *iter = cgroup;
> > > - return cgroup_psi(cgroup);
> > > - }
> > > -#else
> > > - if (*iter)
> > > - return NULL;
> > > + if (cgroup && cgroup_parent(cgroup)) {
> > > + *iter = cgroup;
> > > + return cgroup_psi(cgroup);
> > > + }
> > > #endif
> > > + } else {
> > > + if (*iter)
> > > + return NULL;
> > > + }
> > > *iter = &psi_system;
> > > return &psi_system;
> > > }
> >
> > Hmm. Looks like the case when cgroup_psi_enabled()==true and
> > CONFIG_CGROUPS=n would miss the "if (*iter) return NULL;" condition.
> > Effectively with CONFIG_CGROUPS=n this becomes:
> >
> > if (cgroup_psi_enabled()) { <== assume this is true
> > #ifdef CONFIG_CGROUPS <== compiled out
> > #endif
> > } else {
> > if (*iter) <== this
> > statement will never execute
> > return NULL;
> > }
> > *iter = &psi_system;
> > return &psi_system;
> >
>
> Ah, sorry. I forgot that CONFIG_CGROUPS=n would force
> cgroup_psi_enabled()==false (the way function is defined in cgroup.h),
> so (CONFIG_CGROUPS=n && cgroup_psi_enabled()==true) is an invalid
> configuration. I think adding a comment to your suggestion would make
> it more clear.
> So your suggestion seems to work. I'll test it and include it in the
> next revision. Thanks!
After reworking the code to add a static key I had to expand the
#ifdef CONFIG_CGROUPS section, so I think a code refactoring below
would make sense. It localizes config-specific code and it has the
same exact code for CONFIG_CGROUPS=n and for
cgroup_psi_enabled()==false. WDYT?:
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -181,6 +181,7 @@ struct psi_group psi_system = {
};
static void psi_avgs_work(struct work_struct *work);
+static void cgroup_iterator_init(void);
static void group_init(struct psi_group *group)
{
@@ -211,6 +212,8 @@ void __init psi_init(void)
return;
}
+ cgroup_iterator_init();
+
psi_period = jiffies_to_nsecs(PSI_FREQ);
group_init(&psi_system);
}
@@ -742,11 +745,31 @@ static void psi_group_change(struct psi_group
*group, int cpu,
schedule_delayed_work(&group->avgs_work, PSI_FREQ);
}
-static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
+static inline struct psi_group *sys_group_iterator(struct task_struct *task,
+ void **iter)
{
+ *iter = &psi_system;
+ return &psi_system;
+}
+
#ifdef CONFIG_CGROUPS
+
+DEFINE_STATIC_KEY_FALSE(psi_cgroups_disabled);
+
+static void cgroup_iterator_init(void)
+{
+ if (!cgroup_psi_enabled())
+ static_branch_enable(&psi_cgroups_disabled);
+}
+
+static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
+{
struct cgroup *cgroup = NULL;
+ /* Skip to psi_system if per-cgroup accounting is disabled */
+ if (static_branch_unlikely(&psi_cgroups_disabled))
+ return *iter ? NULL : sys_group_iterator(task, iter);
+
if (!*iter)
cgroup = task->cgroups->dfl_cgrp;
else if (*iter == &psi_system)
@@ -758,14 +781,20 @@ static struct psi_group *iterate_groups(struct
task_struct *task, void **iter)
*iter = cgroup;
return cgroup_psi(cgroup);
}
-#else
- if (*iter)
- return NULL;
-#endif
- *iter = &psi_system;
- return &psi_system;
+
+ return sys_group_iterator(task, iter);
}
+#else /* CONFIG_CGROUPS */
+static inline void cgroup_iterator_init(void) {}
+
+static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
+{
+ return *iter ? NULL : sys_group_iterator(task, iter);
+}
+
+#endif /* CONFIG_CGROUPS */
+
>
>
> > >
> > > --
> > > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@xxxxxxxxxxx.
> > >
