Re: [PATCH v3 1/1] sched/uclamp: add SCHED_FLAG_UTIL_CLAMP_RESET flag to reset uclamp
From: Dietmar Eggemann
Date: Mon Oct 26 2020 - 15:00:55 EST
On 26/10/2020 16:45, Yun Hsiang wrote:
> Hi Dietmar,
>
> On Mon, Oct 26, 2020 at 10:47:11AM +0100, Dietmar Eggemann wrote:
>> On 25/10/2020 08:36, Yun Hsiang wrote:
>>> If the user wants to stop controlling uclamp and let the task inherit
>>> the value from the group, we need a method to reset.
>>>
>>> Add SCHED_FLAG_UTIL_CLAMP_RESET flag to allow the user to reset uclamp via
>>> sched_setattr syscall.
>>>
>>> The policy is
>>> _CLAMP_RESET => reset both min and max
>>> _CLAMP_RESET | _CLAMP_MIN => reset min value
>>> _CLAMP_RESET | _CLAMP_MAX => reset max value
>>> _CLAMP_RESET | _CLAMP_MIN | _CLAMP_MAX => reset both min and max
>>>
>>> Signed-off-by: Yun Hsiang <hsiang023167@xxxxxxxxx>
>>
>> [...]
>>
>>> @@ -1451,7 +1464,8 @@ static void __setscheduler_uclamp(struct task_struct *p,
>>> struct uclamp_se *uc_se = &p->uclamp_req[clamp_id];
>>>
>>> /* Keep using defined clamps across class changes */
>>> - if (uc_se->user_defined)
>>> + if (flags != SCHED_FLAG_UTIL_CLAMP_RESET &&
>>> + uc_se->user_defined)
>>> continue;
>>
>> With:
>>
>> (1) _CLAMP_RESET => reset both min and max
>> (2) _CLAMP_RESET | _CLAMP_MIN => reset min value
>> (3) _CLAMP_RESET | _CLAMP_MAX => reset max value
>> (4) _CLAMP_RESET | _CLAMP_MIN | _CLAMP_MAX => reset both min and max
>>
>> If you reset an RT task with (1) you don't reset its uclamp.min value.
>>
>> __uclamp_update_util_min_rt_default(p) doesn't know about
>> SCHED_FLAG_UTIL_CLAMP_RESET. It only knows user_defined and will bail early.
>>
>
> Sorry I didn't notice __uclamp_update_util_min_rt_default will return
> directly if user_defined is set, I'll fix it.
>
>> [...]
>>
>>> - if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)))
>>> + if (likely(!flags || flags == SCHED_FLAG_UTIL_CLAMP_RESET))
>>> return;
>>>
>>> - if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) {
>>> + if (flags & SCHED_FLAG_UTIL_CLAMP_MIN) {
>>> + if (reset) {
>>> + clamp_value = __default_uclamp_value(p, UCLAMP_MIN);
>>> + user_defined = false;
>>> + } else {
>>> + clamp_value = attr->sched_util_min;
>>> + user_defined = true;
>>> + }
>>
>> Why do you reset for (1) in the for_each_clamp_id(clamp_id) loop and for
>> (2)-(4) in the if (flags & SCHED_FLAG_UTIL_CLAMP_MXX) condition?
>>
>> You could reset (1)-(4) in the for_each_clamp_id(clamp_id) loop? In this
>> case you wouldn't need __default_uclamp_value().
>
> Do you mean adding these code in for_each_clamp_id(clamp_id) loop?
>
> if (clamp_id == UCLAMP_MIN) {
> if (flags == SCHED_FLAG_UTIL_CLAMP_RESET ||
> (reset && (flags || SCHED_FLAG_UTIL_CLAMP_MIN)) ||
> !se->user_defined) {
> if (task_rt(p)) {
> clamp_value = sysctl_sched_uclamp_util_min_rt_default
> } else {
> clamp_value = uclamp_none(clamp_id);
> }
> } else
> continue;
> }
> /* similar code for UCLAMP_MAX */
> ...
> uclamp_se_set(uc_se, clamp_value, false);
>
> It seems more clear.
> If you think this one is better, I'll use this method and send patch V4.
I thought about something like this. Only lightly tested.
---8<---
From: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Date: Mon, 26 Oct 2020 13:52:23 +0100
Subject: [PATCH] SCHED_FLAG_UTIL_CLAMP_RESET
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
---
include/uapi/linux/sched.h | 4 +++-
kernel/sched/core.c | 31 +++++++++++++++++++++++++++----
2 files changed, 30 insertions(+), 5 deletions(-)
diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index 3bac0a8ceab2..0dd890822751 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -132,12 +132,14 @@ struct clone_args {
#define SCHED_FLAG_KEEP_PARAMS 0x10
#define SCHED_FLAG_UTIL_CLAMP_MIN 0x20
#define SCHED_FLAG_UTIL_CLAMP_MAX 0x40
+#define SCHED_FLAG_UTIL_CLAMP_RESET 0x80
#define SCHED_FLAG_KEEP_ALL (SCHED_FLAG_KEEP_POLICY | \
SCHED_FLAG_KEEP_PARAMS)
#define SCHED_FLAG_UTIL_CLAMP (SCHED_FLAG_UTIL_CLAMP_MIN | \
- SCHED_FLAG_UTIL_CLAMP_MAX)
+ SCHED_FLAG_UTIL_CLAMP_MAX | \
+ SCHED_FLAG_UTIL_CLAMP_RESET)
#define SCHED_FLAG_ALL (SCHED_FLAG_RESET_ON_FORK | \
SCHED_FLAG_RECLAIM | \
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3dc415f58bd7..717b1cf5cf1f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1438,6 +1438,23 @@ static int uclamp_validate(struct task_struct *p,
return 0;
}
+static bool uclamp_reset(enum uclamp_id clamp_id, unsigned long flags)
+{
+ if (!(flags & SCHED_FLAG_UTIL_CLAMP_RESET))
+ return false;
+
+ if (!(flags & (SCHED_FLAG_UTIL_CLAMP_MIN | SCHED_FLAG_UTIL_CLAMP_MAX)))
+ return true;
+
+ if ((flags & SCHED_FLAG_UTIL_CLAMP_MIN) && clamp_id == UCLAMP_MIN)
+ return true;
+
+ if ((flags & SCHED_FLAG_UTIL_CLAMP_MAX) && clamp_id == UCLAMP_MAX)
+ return true;
+
+ return false;
+}
+
static void __setscheduler_uclamp(struct task_struct *p,
const struct sched_attr *attr)
{
@@ -1449,24 +1466,30 @@ static void __setscheduler_uclamp(struct task_struct *p,
*/
for_each_clamp_id(clamp_id) {
struct uclamp_se *uc_se = &p->uclamp_req[clamp_id];
+ unsigned int value;
/* Keep using defined clamps across class changes */
- if (uc_se->user_defined)
+ if (!uclamp_reset(clamp_id, attr->sched_flags) &&
+ uc_se->user_defined) {
continue;
+ }
/*
* RT by default have a 100% boost value that could be modified
* at runtime.
*/
if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
- __uclamp_update_util_min_rt_default(p);
+ value = sysctl_sched_uclamp_util_min_rt_default;
else
- uclamp_se_set(uc_se, uclamp_none(clamp_id), false);
+ value = uclamp_none(clamp_id);
+ uclamp_se_set(uc_se, value, false);
}
- if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)))
+ if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)) ||
+ attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_RESET) {
return;
+ }
if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) {
uclamp_se_set(&p->uclamp_req[UCLAMP_MIN],
--
2.17.1