On Mon, May 17, 2021 at 11:31 AM Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
>
> On Sun, May 16, 2021 at 12:52:32PM -0700, Suren Baghdasaryan wrote:
> > 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;
>
> That looks over-engineered. You have to check iter whether cgroups are
> enabled or not. Pulling the jump label check up doesn't save anything,
> but it ends up duplicating code.
>
> What you had in the beginning was better, it just had the system label
> in an unexpected place where it would check iter twice in a row.
>
> The (*iter == &psi_system) check inside the cgroups branch has the
> same purpose as the (*iter) check in the else branch. We could
> consolidate that by pulling it up front.
>
> If we wrap the entire cgroup iteration block into the static branch,
> IMO it becomes a bit clearer as well.
>
> How about this?
>
> 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)) {
> 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;
> }
This looks great to me. Will use it in the next version. Thanks!
