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Message-ID: <CAKfTPtDuCJTOJ0WvtEJLmkanZCWLfKG-D5r8+8p7EWGin2mGRw@mail.gmail.com>
Date: Sat, 8 Feb 2025 20:32:38 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: zihan zhou <15645113830zzh@...il.com>
Cc: bsegall@...gle.com, dietmar.eggemann@....com, juri.lelli@...hat.com,
linux-kernel@...r.kernel.org, mgorman@...e.de, mingo@...hat.com,
peterz@...radead.org, rostedt@...dmis.org, vschneid@...hat.com
Subject: Re: [PATCH V3 2/2] sched: Reduce the default slice to avoid tasks
getting an extra tick
On Sat, 8 Feb 2025 at 08:59, zihan zhou <15645113830zzh@...il.com> wrote:
>
> Update sysctl_sched_base_slice with debugfs, limit its value and
> update normalized_sysctl_sched_base_slice.
>
> Rename the function sched_update_scaling to sched_update_scaling_or_slice,
> it is no longer related to CONFIG_SMP and return void, as the previous
> function always returns 0 and there is no need to judge the return value
> again, just like the function update_sysctl.
>
> Signed-off-by: zihan zhou <15645113830zzh@...il.com>
> Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
My Reviewed applied only for patch 1 not patch 2. That's also why I
asked you to split it. Patch 1 makes sense for me but I don't see the
benefit of patch 2
> ---
> kernel/sched/debug.c | 52 +++++++++++++++++++++++++++++++++++++++++---
> kernel/sched/fair.c | 8 +++----
> kernel/sched/sched.h | 4 ++--
> 3 files changed, 54 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index fd7e85220715..f40d9d638939 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -166,6 +166,53 @@ static const struct file_operations sched_feat_fops = {
> .release = single_release,
> };
>
> +static ssize_t sched_base_slice_write(struct file *filp, const char __user *ubuf,
> + size_t cnt, loff_t *ppos)
> +{
> + char buf[16];
> + unsigned int base_slice;
> +
> + if (cnt > 15)
> + cnt = 15;
> +
> + if (copy_from_user(&buf, ubuf, cnt))
> + return -EFAULT;
> + buf[cnt] = '\0';
> +
> + if (kstrtouint(buf, 10, &base_slice))
> + return -EINVAL;
> +
> + base_slice = clamp_t(u64, base_slice,
> + NSEC_PER_MSEC/10, /* HZ=1000 * 10 */
> + NSEC_PER_MSEC*100); /* HZ=100 / 10 */
> +
> + sysctl_sched_base_slice = base_slice;
> +
> + sched_update_scaling_or_slice();
> +
> + *ppos += cnt;
> + return cnt;
> +}
> +
> +static int sched_base_slice_show(struct seq_file *m, void *v)
> +{
> + seq_printf(m, "%d\n", sysctl_sched_base_slice);
> + return 0;
> +}
> +
> +static int sched_base_slice_open(struct inode *inode, struct file *filp)
> +{
> + return single_open(filp, sched_base_slice_show, NULL);
> +}
> +
> +static const struct file_operations sched_base_slice_fops = {
> + .open = sched_base_slice_open,
> + .write = sched_base_slice_write,
> + .read = seq_read,
> + .llseek = seq_lseek,
> + .release = single_release,
> +};
> +
> #ifdef CONFIG_SMP
>
> static ssize_t sched_scaling_write(struct file *filp, const char __user *ubuf,
> @@ -188,8 +235,7 @@ static ssize_t sched_scaling_write(struct file *filp, const char __user *ubuf,
> return -EINVAL;
>
> sysctl_sched_tunable_scaling = scaling;
> - if (sched_update_scaling())
> - return -EINVAL;
> + sched_update_scaling_or_slice();
>
> *ppos += cnt;
> return cnt;
> @@ -505,7 +551,7 @@ static __init int sched_init_debug(void)
> debugfs_create_file("preempt", 0644, debugfs_sched, NULL, &sched_dynamic_fops);
> #endif
>
> - debugfs_create_u32("base_slice_ns", 0644, debugfs_sched, &sysctl_sched_base_slice);
> + debugfs_create_file("base_slice_ns", 0644, debugfs_sched, NULL, &sched_base_slice_fops);
>
> debugfs_create_u32("latency_warn_ms", 0644, debugfs_sched, &sysctl_resched_latency_warn_ms);
> debugfs_create_u32("latency_warn_once", 0644, debugfs_sched, &sysctl_resched_latency_warn_once);
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 34e7d09320f7..0fe7c4530a87 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -981,8 +981,8 @@ struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
> /**************************************************************
> * Scheduling class statistics methods:
> */
> -#ifdef CONFIG_SMP
> -int sched_update_scaling(void)
> +
> +void sched_update_scaling_or_slice(void)
> {
> unsigned int factor = get_update_sysctl_factor();
>
> @@ -990,10 +990,8 @@ int sched_update_scaling(void)
> (normalized_sysctl_##name = sysctl_##name / (factor))
> WRT_SYSCTL(sched_base_slice);
> #undef WRT_SYSCTL
> -
> - return 0;
> }
> -#endif
> +
> #endif
>
> static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se);
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index c7cf4cc57cdd..3ac73cbd711f 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1923,6 +1923,8 @@ init_numa_balancing(unsigned long clone_flags, struct task_struct *p)
>
> #endif /* !CONFIG_NUMA_BALANCING */
>
> +extern void sched_update_scaling_or_slice(void);
> +
> #ifdef CONFIG_SMP
>
> static inline void
> @@ -2088,8 +2090,6 @@ static inline void update_sched_domain_debugfs(void) { }
> static inline void dirty_sched_domain_sysctl(int cpu) { }
> #endif
>
> -extern int sched_update_scaling(void);
> -
> static inline const struct cpumask *task_user_cpus(struct task_struct *p)
> {
> if (!p->user_cpus_ptr)
> --
> 2.33.0
>
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