[v1] sched/balancing: Misc updates & cleanups

[PATCH 08/10] sched/balancing: Update run_rebalance_domains() comments

Posted by Ingo Molnar 1 year, 11 months ago

The first sentence of the comment explaining run_rebalance_domains()
is historic and not true anymore:

    * run_rebalance_domains is triggered when needed from the scheduler tick.

... contradicted/modified by the second sentence:

    * Also triggered for NOHZ idle balancing (with NOHZ_BALANCE_KICK set).

Avoid that kind of confusion straight away and explain from what
places sched_balance_softirq() is triggered.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
---
 kernel/sched/fair.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f3c03c6db3c8..b567c0790f44 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12409,9 +12409,12 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
 }
 
 /*
- * This softirq may be triggered from the scheduler tick, or by
- * any of the flags in NOHZ_KICK_MASK: NOHZ_BALANCE_KICK,
- * NOHZ_STATS_KICK or NOHZ_NEXT_KICK.
+ * This softirq handler is triggered via SCHED_SOFTIRQ from two places:
+ *
+ * - directly from the local scheduler_tick() for periodic load balancing
+ *
+ * - indirectly from a remote scheduler_tick() for NOHZ idle balancing
+ *   through the SMP cross-call nohz_csd_func()
  */
 static __latent_entropy void run_rebalance_domains(struct softirq_action *h)
 {
-- 
2.40.1

Re: [PATCH 08/10] sched/balancing: Update run_rebalance_domains() comments

Posted by Vincent Guittot 1 year, 11 months ago

On Fri, 8 Mar 2024 at 11:59, Ingo Molnar <mingo@kernel.org> wrote:
>
> The first sentence of the comment explaining run_rebalance_domains()
> is historic and not true anymore:
>
>     * run_rebalance_domains is triggered when needed from the scheduler tick.
>
> ... contradicted/modified by the second sentence:
>
>     * Also triggered for NOHZ idle balancing (with NOHZ_BALANCE_KICK set).
>
> Avoid that kind of confusion straight away and explain from what
> places sched_balance_softirq() is triggered.
>
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>

Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>

> ---
>  kernel/sched/fair.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index f3c03c6db3c8..b567c0790f44 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -12409,9 +12409,12 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
>  }
>
>  /*
> - * This softirq may be triggered from the scheduler tick, or by
> - * any of the flags in NOHZ_KICK_MASK: NOHZ_BALANCE_KICK,
> - * NOHZ_STATS_KICK or NOHZ_NEXT_KICK.
> + * This softirq handler is triggered via SCHED_SOFTIRQ from two places:
> + *
> + * - directly from the local scheduler_tick() for periodic load balancing
> + *
> + * - indirectly from a remote scheduler_tick() for NOHZ idle balancing
> + *   through the SMP cross-call nohz_csd_func()
>   */
>  static __latent_entropy void run_rebalance_domains(struct softirq_action *h)
>  {
> --
> 2.40.1
>

[tip: sched/core] sched/balancing: Update run_rebalance_domains() comments

Posted by tip-bot2 for Ingo Molnar 1 year, 11 months ago

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     3dc6f6c8efe2d9148865664fffbe9dd89fb0d157
Gitweb:        https://git.kernel.org/tip/3dc6f6c8efe2d9148865664fffbe9dd89fb0d157
Author:        Ingo Molnar <mingo@kernel.org>
AuthorDate:    Fri, 08 Mar 2024 11:58:59 +01:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 12 Mar 2024 11:59:43 +01:00

sched/balancing: Update run_rebalance_domains() comments

The first sentence of the comment explaining run_rebalance_domains()
is historic and not true anymore:

    * run_rebalance_domains is triggered when needed from the scheduler tick.

... contradicted/modified by the second sentence:

    * Also triggered for NOHZ idle balancing (with NOHZ_BALANCE_KICK set).

Avoid that kind of confusion straight away and explain from what
places sched_balance_softirq() is triggered.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Acked-by: Valentin Schneider <vschneid@redhat.com>
Link: https://lore.kernel.org/r/20240308105901.1096078-9-mingo@kernel.org
---
 kernel/sched/fair.c |  9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f3c03c6..b567c07 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12409,9 +12409,12 @@ out:
 }
 
 /*
- * This softirq may be triggered from the scheduler tick, or by
- * any of the flags in NOHZ_KICK_MASK: NOHZ_BALANCE_KICK,
- * NOHZ_STATS_KICK or NOHZ_NEXT_KICK.
+ * This softirq handler is triggered via SCHED_SOFTIRQ from two places:
+ *
+ * - directly from the local scheduler_tick() for periodic load balancing
+ *
+ * - indirectly from a remote scheduler_tick() for NOHZ idle balancing
+ *   through the SMP cross-call nohz_csd_func()
  */
 static __latent_entropy void run_rebalance_domains(struct softirq_action *h)
 {