From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Qais Yousef <qais.yousef@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Jonathan Corbet <corbet@lwn.net>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Luis Chamberlain <mcgrof@kernel.org>,
Kees Cook <keescook@chromium.org>,
Iurii Zaikin <yzaikin@google.com>,
Quentin Perret <qperret@google.com>,
Valentin Schneider <valentin.schneider@arm.com>,
Patrick Bellasi <patrick.bellasi@matbug.net>,
Pavan Kondeti <pkondeti@codeaurora.org>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 1/2] sched/uclamp: Add a new sysctl to control RT default boost value
Date: Wed, 22 Apr 2020 12:59:47 +0200 [thread overview]
Message-ID: <45236ccd-24d2-3b99-cd9b-bac13cfaceab@arm.com> (raw)
In-Reply-To: <20200421112733.4jbguidgbqwzhv23@e107158-lin.cambridge.arm.com>
On 21/04/2020 13:27, Qais Yousef wrote:
> On 04/21/20 13:18, Dietmar Eggemann wrote:
>> On 20/04/2020 17:13, Qais Yousef wrote:
>>> On 04/20/20 10:29, Dietmar Eggemann wrote:
>>>> On 03.04.20 14:30, Qais Yousef wrote:
>>>>
>>>> [...]
>>>>
>>>>> @@ -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];
>>>>> +
>>>>> + if (!uc_se->user_defined)
>>>>> + uclamp_se_set(uc_se, sysctl_sched_rt_default_uclamp_util_min, false);
>>>>> +}
>>>>> +
>>>>> 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);
>>>>> +
>>>>
>>>> Does this have to be an extra function? Can we not reuse
>>>> uclamp_tg_restrict() by slightly rename it to uclamp_restrict()?
Btw, there was an issue in my little snippet. I used uc_req.user_defined
uninitialized in uclamp_restrict().
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f3706dad32ce..7e6b2b7cd1e5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -903,12 +903,11 @@ uclamp_restrict(struct task_struct *p, enum uclamp_id clamp_id)
{
struct uclamp_se uc_req, __maybe_unused uc_max;
- if (unlikely(rt_task(p)) && clamp_id == UCLAMP_MIN &&
- !uc_req.user_defined) {
+ if (unlikely(rt_task(p)) && clamp_id == UCLAMP_MIN) {
struct uclamp_se *uc_se = &p->uclamp_req[UCLAMP_MIN];
int rt_min = sysctl_sched_rt_default_uclamp_util_min;
- if (uc_se->value != rt_min) {
+ if (!uc_se->user_defined && uc_se->value != rt_min) {
uclamp_se_set(uc_se, rt_min, false);
printk("uclamp_restrict() [%s %d] p->uclamp_req[%d].value=%d\n",
p->comm, p->pid, clamp_id, uc_se->value);
>>> Hmm the thing is that we're not restricting here. In contrary we're boosting,
>>> so the name would be misleading.
>>
>> I always thought that we're restricting p->uclamp_req[UCLAMP_MIN].value (default 1024) to
>> sysctl_sched_rt_default_uclamp_util_min (0-1024)?
>
> The way I look at it is that we're *setting* it to
> sysctl_sched_rt_default_uclamp_util_min if !user_defined.
>
> The restriction mechanism that ensures this set value doesn't escape
> cgroup/global restrictions setup.
I guess we overall agree here.
I see 3 restriction levels: (!user_defined) task -> taskgroup -> system
I see sysctl_sched_rt_default_uclamp_util_min (min_rt_default) as a
restriction on task level.
It's true that the task level restriction is setting the value at the same time.
For CFS (id=UCLAMP_[MIN\|MAX]) and RT (id=UCLAMP_MAX) we use
uclamp_none(id) and those values (0, 1024) are fixed so these task level
values don't need to be further restricted.
For RT (id=UCLAMP_MIN) we use 'min_rt_default' and since it can change
we have to check the task level restriction in 'uclamp_eff_get() ->
uclamp_(tg)_restrict()'.
root@h960:~# echo 999 > /proc/sys/kernel/sched_rt_default_util_clamp_min
[ 2540.507236] uclamp_eff_get() [rtkit-daemon 419] tag=0 uclamp_id=0 uc_req.value=1024
[ 2540.514947] uclamp_eff_get() [rtkit-daemon 419] tag=1 uclamp_id=0 uc_req.value=1024
[ 2548.015208] uclamp_restrict() [rtkit-daemon 419] p->uclamp_req[0].value=999
root@h960:~# echo 666 > /proc/sys/kernel/sched_util_clamp_min
[ 2548.022219] uclamp_eff_get() [rtkit-daemon 419] tag=0 uclamp_id=0 uc_req.value=999
[ 2548.029825] uclamp_eff_get() [rtkit-daemon 419] tag=1 uclamp_id=0 uc_req.value=999
[ 2553.479509] uclamp_eff_get() [rtkit-daemon 419] tag=0 uclamp_id=0 uc_max.value=666
[ 2553.487131] uclamp_eff_get() [rtkit-daemon 419] tag=1 uclamp_id=0 uc_max.value=666
Haven't tried to put an rt task into a taskgroup other than root.
next prev parent reply other threads:[~2020-04-22 11:00 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-03 12:30 [PATCH 1/2] sched/uclamp: Add a new sysctl to control RT default boost value Qais Yousef
2020-04-03 12:30 ` [PATCH 2/2] Documentation/sysctl: Document uclamp sysctl knobs Qais Yousef
2020-04-14 18:21 ` [PATCH 1/2] sched/uclamp: Add a new sysctl to control RT default boost value Patrick Bellasi
2020-04-15 7:46 ` Patrick Bellasi
2020-04-20 15:04 ` Qais Yousef
2020-04-20 8:24 ` Dietmar Eggemann
2020-04-20 15:19 ` Qais Yousef
2020-04-21 0:52 ` Steven Rostedt
2020-04-21 11:16 ` Dietmar Eggemann
2020-04-21 11:23 ` Qais Yousef
2020-04-20 14:50 ` Qais Yousef
2020-04-15 10:11 ` Quentin Perret
2020-04-20 15:08 ` Qais Yousef
2020-04-20 8:29 ` Dietmar Eggemann
2020-04-20 15:13 ` Qais Yousef
2020-04-21 11:18 ` Dietmar Eggemann
2020-04-21 11:27 ` Qais Yousef
2020-04-22 10:59 ` Dietmar Eggemann [this message]
2020-04-22 13:13 ` Qais Yousef
2020-05-11 15:40 Qais Yousef
2020-05-11 17:18 ` Qais Yousef
2020-05-12 2:10 ` Pavan Kondeti
2020-05-12 11:46 ` Qais Yousef
2020-05-15 11:08 ` Patrick Bellasi
2020-05-18 8:31 ` Dietmar Eggemann
2020-05-18 16:49 ` Qais Yousef
2020-05-28 13:23 ` Peter Zijlstra
2020-05-28 15:58 ` Qais Yousef
2020-05-28 16:11 ` Peter Zijlstra
2020-05-28 16:51 ` Qais Yousef
2020-05-28 18:29 ` Peter Zijlstra
2020-05-28 19:08 ` Patrick Bellasi
2020-05-28 19:20 ` Dietmar Eggemann
2020-05-29 9:11 ` Qais Yousef
2020-05-29 10:21 ` Mel Gorman
2020-05-29 15:11 ` Qais Yousef
2020-05-29 16:02 ` Mel Gorman
2020-05-29 16:05 ` Qais Yousef
2020-05-29 10:08 ` Mel Gorman
2020-05-29 16:04 ` Qais Yousef
2020-05-29 16:57 ` Mel Gorman
2020-06-02 16:46 ` Dietmar Eggemann
2020-06-03 8:29 ` Patrick Bellasi
2020-06-03 10:10 ` Mel Gorman
2020-06-03 14:59 ` Vincent Guittot
2020-06-03 16:52 ` Qais Yousef
2020-06-04 12:14 ` Vincent Guittot
2020-06-05 10:45 ` Qais Yousef
2020-06-09 15:29 ` Vincent Guittot
2020-06-08 12:31 ` Qais Yousef
2020-06-08 13:06 ` Valentin Schneider
2020-06-08 14:44 ` Steven Rostedt
2020-06-11 10:13 ` Qais Yousef
2020-06-09 17:10 ` Vincent Guittot
2020-06-11 10:24 ` Qais Yousef
2020-06-11 12:01 ` Vincent Guittot
2020-06-23 15:44 ` Qais Yousef
2020-06-24 8:45 ` Vincent Guittot
2020-06-05 7:55 ` Patrick Bellasi
2020-06-05 11:32 ` Qais Yousef
2020-06-05 13:27 ` Patrick Bellasi
2020-06-03 9:40 ` Mel Gorman
2020-06-03 12:41 ` Qais Yousef
2020-06-04 13:40 ` Mel Gorman
2020-06-05 10:58 ` Qais Yousef
2020-06-11 10:58 ` Qais Yousef
2020-06-16 11:08 ` Qais Yousef
2020-06-16 13:56 ` Lukasz Luba
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