From: Kairui Song <kasong@tencent.com>

Since the only case where cgroup_psi should return psi_system instead of
the cgroup's psi_group is the root cgroup, just set root cgroup's psi to
point to psi_system to remove the if branch.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
 include/linux/psi.h    | 2 +-
 kernel/cgroup/cgroup.c | 7 ++++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/psi.h b/include/linux/psi.h
index b029a847def1..9c3a1638b618 100644
--- a/include/linux/psi.h
+++ b/include/linux/psi.h
@@ -33,7 +33,7 @@ __poll_t psi_trigger_poll(void **trigger_ptr, struct file *file,
 #ifdef CONFIG_CGROUPS
 static inline struct psi_group *cgroup_psi(struct cgroup *cgrp)
 {
-	return cgroup_ino(cgrp) == 1 ? &psi_system : cgrp->psi;
+	return cgrp->psi;
 }
 
 int psi_cgroup_alloc(struct cgroup *cgrp);
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index c099cf3fa02d..1491d63b06b6 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -163,7 +163,12 @@ static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
 static DEFINE_PER_CPU(struct cgroup_rstat_cpu, cgrp_dfl_root_rstat_cpu);
 
 /* the default hierarchy */
-struct cgroup_root cgrp_dfl_root = { .cgrp.rstat_cpu = &cgrp_dfl_root_rstat_cpu };
+struct cgroup_root cgrp_dfl_root = {
+	.cgrp.rstat_cpu = &cgrp_dfl_root_rstat_cpu,
+#ifdef CONFIG_PSI
+	.cgrp.psi = &psi_system
+#endif
+};
 EXPORT_SYMBOL_GPL(cgrp_dfl_root);
 
 /*
-- 
2.39.1

Hello Kairui,

On Thu, Feb 09, 2023 at 12:16:53AM +0800, Kairui Song wrote:
> From: Kairui Song <kasong@tencent.com>
> 
> Since the only case where cgroup_psi should return psi_system instead of
> the cgroup's psi_group is the root cgroup, just set root cgroup's psi to
> point to psi_system to remove the if branch.
> 
> Signed-off-by: Kairui Song <kasong@tencent.com>

Thanks for the patches. They overall look good, and the numbers even
better.

>  include/linux/psi.h    | 2 +-
>  kernel/cgroup/cgroup.c | 7 ++++++-
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/psi.h b/include/linux/psi.h
> index b029a847def1..9c3a1638b618 100644
> --- a/include/linux/psi.h
> +++ b/include/linux/psi.h
> @@ -33,7 +33,7 @@ __poll_t psi_trigger_poll(void **trigger_ptr, struct file *file,
>  #ifdef CONFIG_CGROUPS
>  static inline struct psi_group *cgroup_psi(struct cgroup *cgrp)
>  {
> -	return cgroup_ino(cgrp) == 1 ? &psi_system : cgrp->psi;
> +	return cgrp->psi;
>  }
>  
>  int psi_cgroup_alloc(struct cgroup *cgrp);
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index c099cf3fa02d..1491d63b06b6 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -163,7 +163,12 @@ static struct static_key_true *cgroup_subsys_on_dfl_key[] = {
>  static DEFINE_PER_CPU(struct cgroup_rstat_cpu, cgrp_dfl_root_rstat_cpu);
>  
>  /* the default hierarchy */
> -struct cgroup_root cgrp_dfl_root = { .cgrp.rstat_cpu = &cgrp_dfl_root_rstat_cpu };
> +struct cgroup_root cgrp_dfl_root = {
> +	.cgrp.rstat_cpu = &cgrp_dfl_root_rstat_cpu,
> +#ifdef CONFIG_PSI
> +	.cgrp.psi = &psi_system
> +#endif

Nitpick: customary coding style is to keep a comma even after the last
entry in the struct. Somebody appending new things won't need to touch
the previous last line, which adds diff noise.

With that, please add:

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

On Thu, Feb 09, 2023 at 12:16:53AM +0800, Kairui Song <ryncsn@gmail.com> wrote:
>  include/linux/psi.h    | 2 +-
>  kernel/cgroup/cgroup.c | 7 ++++++-
>  2 files changed, 7 insertions(+), 2 deletions(-)

Reviewed-by: Michal Koutný <mkoutny@suse.com>