2022-03-02 10:40:59

by CGEL

Subject: [PATCH] sched/topology: avoid calling synchronize_rcu()

From: Lv Ruyi (CGEL ZTE) <[email protected]>

Kfree_rcu() usually results in even simpler code than does
synchronize_rcu() without synchronize_rcu()'s multi-millisecond
latency, so replace synchronize_rcu() with kfree_rcu().

Reported-by: Zeal Robot <[email protected]>
Signed-off-by: Lv Ruyi (CGEL ZTE) <[email protected]>
---
kernel/sched/topology.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 974212620fa1..0ce302b4d732 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1970,8 +1970,7 @@ static void sched_reset_numa(void)
if (distances || masks) {
int i, j;

- synchronize_rcu();
- kfree(distances);
+ kfree_rcu(distances);
for (i = 0; i < nr_levels && masks; i++) {
if (!masks[i])
continue;
--
2.25.1

2022-03-02 22:31:23

by Valentin Schneider

Subject: Re: [PATCH] sched/topology: avoid calling synchronize_rcu()

On 02/03/22 01:14, [email protected] wrote:
> From: Lv Ruyi (CGEL ZTE) <[email protected]>
>
> Kfree_rcu() usually results in even simpler code than does
> synchronize_rcu() without synchronize_rcu()'s multi-millisecond
> latency, so replace synchronize_rcu() with kfree_rcu().
>
> Reported-by: Zeal Robot <[email protected]>
> Signed-off-by: Lv Ruyi (CGEL ZTE) <[email protected]>
> ---
> kernel/sched/topology.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 974212620fa1..0ce302b4d732 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -1970,8 +1970,7 @@ static void sched_reset_numa(void)
> if (distances || masks) {
> int i, j;
>
> - synchronize_rcu();
> - kfree(distances);
> + kfree_rcu(distances);

What about the freeing of the cpumasks below? You don't want to free those
before the end of the grace period either. With that in mind, I think the
current synchronize_rcu() + batch of kfree()'s is fine, it's a slow path
anyway (hotplug).


> for (i = 0; i < nr_levels && masks; i++) {
> if (!masks[i])
> continue;
> --
> 2.25.1