Hi Qais!
On 03-Apr 13:30, Qais Yousef wrote:
[...]
> diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h
> index d4f6215ee03f..91204480fabc 100644
> --- a/include/linux/sched/sysctl.h
> +++ b/include/linux/sched/sysctl.h
> @@ -59,6 +59,7 @@ extern int sysctl_sched_rt_runtime;
> #ifdef CONFIG_UCLAMP_TASK
> extern unsigned int sysctl_sched_uclamp_util_min;
> extern unsigned int sysctl_sched_uclamp_util_max;
> +extern unsigned int sysctl_sched_rt_default_uclamp_util_min;
nit-pick: I would prefer to keep the same prefix of the already
exising knobs, i.e. sysctl_sched_uclamp_util_min_rt
The same change for consistency should be applied to all the following
symbols related to "uclamp_util_min_rt".
NOTE: I would not use "default" as I think that what we are doing is
exactly force setting a user_defined value for all RT tasks. More on
that later...
> #endif
>
> #ifdef CONFIG_CFS_BANDWIDTH
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 1a9983da4408..a726b26a5056 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -797,6 +797,27 @@ unsigned int sysctl_sched_uclamp_util_min = SCHED_CAPACITY_SCALE;
> /* Max allowed maximum utilization */
> unsigned int sysctl_sched_uclamp_util_max = SCHED_CAPACITY_SCALE;
>
> +/*
> + * By default RT tasks run at the maximum performance point/capacity of the
> + * system. Uclamp enforces this by always setting UCLAMP_MIN of RT tasks to
> + * SCHED_CAPACITY_SCALE.
> + *
> + * This knob allows admins to change the default behavior when uclamp is being
> + * used. In battery powered devices, particularly, running at the maximum
> + * capacity and frequency will increase energy consumption and shorten the
> + * battery life.
> + *
> + * This knob only affects the default value RT has when a new RT task is
> + * forked or has just changed policy to RT, given the user hasn't modified the
> + * uclamp.min value of the task via sched_setattr().
> + *
> + * This knob will not override the system default sched_util_clamp_min defined
> + * above.
> + *
> + * Any modification is applied lazily on the next RT task wakeup.
> + */
> +unsigned int sysctl_sched_rt_default_uclamp_util_min = SCHED_CAPACITY_SCALE;
> +
> /* All clamps are required to be less or equal than these values */
> static struct uclamp_se uclamp_default[UCLAMP_CNT];
>
> @@ -924,6 +945,14 @@ uclamp_eff_get(struct task_struct *p, enum uclamp_id clamp_id)
> return uc_req;
> }
>
> +static void uclamp_rt_sync_default_util_min(struct task_struct *p)
> +{
> + struct uclamp_se *uc_se = &p->uclamp_req[UCLAMP_MIN];
Don't we have to filter for RT tasks only here?
> +
> + if (!uc_se->user_defined)
> + uclamp_se_set(uc_se, sysctl_sched_rt_default_uclamp_util_min, false);
Here you are actually setting a user-requested value, why not marking
it as that, i.e. by using true for the last parameter?
Moreover, by keeping user_defined=false I think you are not getting
what you want for RT tasks running in a nested cgroup.
Let say a subgroup is still with the util_min=1024 inherited from the
system defaults, in uclamp_tg_restrict() we will still return the max
value and not what you requested for. Isn't it?
IOW, what about:
---8<---
static void uclamp_sync_util_min_rt(struct task_struct *p)
{
struct uclamp_se *uc_se = &p->uclamp_req[UCLAMP_MIN];
if (likely(uc_se->user_defined || !rt_task(p)))
return;
uclamp_se_set(uc_se, sysctl_sched_uclamp_util_min_rt, true);
}
---8<---
> +}
> +
> unsigned long uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id)
> {
> struct uclamp_se uc_eff;
> @@ -1030,6 +1059,12 @@ static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
> if (unlikely(!p->sched_class->uclamp_enabled))
> return;
>
> + /*
> + * When sysctl_sched_rt_default_uclamp_util_min value is changed by the
> + * user, we apply any new value on the next wakeup, which is here.
> + */
> + uclamp_rt_sync_default_util_min(p);
> +
> for_each_clamp_id(clamp_id)
> uclamp_rq_inc_id(rq, p, clamp_id);
>
> @@ -1121,12 +1156,13 @@ int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
> loff_t *ppos)
> {
> bool update_root_tg = false;
> - int old_min, old_max;
> + int old_min, old_max, old_rt_min;
> int result;
>
> mutex_lock(&uclamp_mutex);
> old_min = sysctl_sched_uclamp_util_min;
> old_max = sysctl_sched_uclamp_util_max;
> + old_rt_min = sysctl_sched_rt_default_uclamp_util_min;
Perpahs it's just my OCD but, is not "old_min_rt" reading better?
>
> result = proc_dointvec(table, write, buffer, lenp, ppos);
> if (result)
> @@ -1134,12 +1170,23 @@ int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
> if (!write)
> goto done;
>
> + /*
> + * The new value will be applied to all RT tasks the next time they
> + * wakeup, assuming the task is using the system default and not a user
> + * specified value. In the latter we shall leave the value as the user
> + * requested.
> + */
Should not this comment go before the next block?
> if (sysctl_sched_uclamp_util_min > sysctl_sched_uclamp_util_max ||
> sysctl_sched_uclamp_util_max > SCHED_CAPACITY_SCALE) {
> result = -EINVAL;
> goto undo;
> }
>
> + if (sysctl_sched_rt_default_uclamp_util_min > SCHED_CAPACITY_SCALE) {
> + result = -EINVAL;
> + goto undo;
> + }
> +
> if (old_min != sysctl_sched_uclamp_util_min) {
> uclamp_se_set(&uclamp_default[UCLAMP_MIN],
> sysctl_sched_uclamp_util_min, false);
> @@ -1165,6 +1212,7 @@ int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
> undo:
> sysctl_sched_uclamp_util_min = old_min;
> sysctl_sched_uclamp_util_max = old_max;
> + sysctl_sched_rt_default_uclamp_util_min = old_rt_min;
> done:
> mutex_unlock(&uclamp_mutex);
>
> @@ -1207,9 +1255,13 @@ static void __setscheduler_uclamp(struct task_struct *p,
> if (uc_se->user_defined)
> continue;
>
> - /* By default, RT tasks always get 100% boost */
> + /*
> + * By default, RT tasks always get 100% boost, which the admins
> + * are allowed to change via
> + * sysctl_sched_rt_default_uclamp_util_min knob.
> + */
> if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
> - clamp_value = uclamp_none(UCLAMP_MAX);
> + clamp_value = sysctl_sched_rt_default_uclamp_util_min;
>
> uclamp_se_set(uc_se, clamp_value, false);
> }
> @@ -1241,9 +1293,13 @@ static void uclamp_fork(struct task_struct *p)
> for_each_clamp_id(clamp_id) {
> unsigned int clamp_value = uclamp_none(clamp_id);
>
> - /* By default, RT tasks always get 100% boost */
> + /*
> + * By default, RT tasks always get 100% boost, which the admins
> + * are allowed to change via
> + * sysctl_sched_rt_default_uclamp_util_min knob.
> + */
> if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
> - clamp_value = uclamp_none(UCLAMP_MAX);
> + clamp_value = sysctl_sched_rt_default_uclamp_util_min;
>
This is not required, look at this Quentin's patch:
Message-ID: <20200414161320.251897-1-qperret@xxxxxxxxxx>
https://lore.kernel.org/lkml/20200414161320.251897-1-qperret@xxxxxxxxxx/
> uclamp_se_set(&p->uclamp_req[clamp_id], clamp_value, false);
> }
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index ad5b88a53c5a..0272ae8c6147 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -465,6 +465,13 @@ static struct ctl_table kern_table[] = {
> .mode = 0644,
> .proc_handler = sysctl_sched_uclamp_handler,
> },
> + {
> + .procname = "sched_rt_default_util_clamp_min",
> + .data = &sysctl_sched_rt_default_uclamp_util_min,
> + .maxlen = sizeof(unsigned int),
> + .mode = 0644,
> + .proc_handler = sysctl_sched_uclamp_handler,
> + },
> #endif
> #ifdef CONFIG_SCHED_AUTOGROUP
> {
Best,
Patrick
--
#include <best/regards.h>
Patrick Bellasi
