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Date: Thu, 17 Jun 2021 10:02:19 +0100
From: Qais Yousef <qais.yousef@....com>
To: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
Patrick Bellasi <patrick.bellasi@...bug.net>,
Tejun Heo <tj@...nel.org>, Quentin Perret <qperret@...gle.com>,
Wei Wang <wvw@...gle.com>, Yun Hsiang <hsiang023167@...il.com>,
Xuewen Yan <xuewen.yan94@...il.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/uclamp: Fix uclamp_tg_restrict()
On 06/16/21 19:09, Dietmar Eggemann wrote:
> On 11/06/2021 14:22, Qais Yousef wrote:
> > Now cpu.uclamp.min acts as a protection, we need to make sure that the
> > uclamp request of the task is within the allowed range of the cgroup,
> > that is it is clamp()'ed correctly by tg->uclamp[UCLAMP_MIN] and
> > tg->uclamp[UCLAMP_MAX].
> >
> > As reported by Xuewen [1] we can have some corner cases where there's
> > inverstion between uclamp requested by task (p) and the uclamp values of
>
> s/inverstion/inversion
Fixed.
>
> [...]
>
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 9e9a5be35cde..0318b00baa97 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -1403,38 +1403,28 @@ static void uclamp_sync_util_min_rt_default(void)
> > static inline struct uclamp_se
> > uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
> > {
> > - struct uclamp_se uc_req = p->uclamp_req[clamp_id];
> > + /* Copy by value as we could modify it */
> > + struct uclamp_se uc_eff = p->uclamp_req[clamp_id];
> > #ifdef CONFIG_UCLAMP_TASK_GROUP
> > + unsigned int tg_min, tg_max, value;
> >
> > /*
> > * Tasks in autogroups or root task group will be
> > * restricted by system defaults.
> > */
> > if (task_group_is_autogroup(task_group(p)))
> > - return uc_req;
> > + return uc_eff;
> > if (task_group(p) == &root_task_group)
> > - return uc_req;
> > + return uc_eff;
> >
> > - switch (clamp_id) {
> > - case UCLAMP_MIN: {
> > - struct uclamp_se uc_min = task_group(p)->uclamp[clamp_id];
> > - if (uc_req.value < uc_min.value)
> > - return uc_min;
> > - break;
> > - }
> > - case UCLAMP_MAX: {
> > - struct uclamp_se uc_max = task_group(p)->uclamp[clamp_id];
> > - if (uc_req.value > uc_max.value)
> > - return uc_max;
> > - break;
> > - }
> > - default:
> > - WARN_ON_ONCE(1);
> > - break;
> > - }
> > + tg_min = task_group(p)->uclamp[UCLAMP_MIN].value;
> > + tg_max = task_group(p)->uclamp[UCLAMP_MAX].value;
> > + value = uc_eff.value;
> > + value = clamp(value, tg_min, tg_max);
> > + uclamp_se_set(&uc_eff, value, false);
> > #endif
> >
> > - return uc_req;
> > + return uc_eff;
> > }
>
> I got confused by the renaming uc_req -> uc_eff.
>
> We have:
>
> uclamp_eff_value() (1)
>
> uclamp_se uc_eff = uclamp_eff_get(p, clamp_id); (2)
>
> uclamp_se uc_req = uclamp_tg_restrict(p, clamp_id) (3)
>
> struct uclamp_se uc_eff = p->uclamp_req[clamp_id];
> ....
>
> (3) is now calling it uc_eff where (2) still uses uc_req for the return
> of (3). IMHO uc_*eff* was used after the system level (
> uclamp_default) have been applied.
Renamed it back to uc_req.
>
> [...]
>
> > @@ -1670,10 +1659,8 @@ uclamp_update_active_tasks(struct cgroup_subsys_state *css,
> >
> > css_task_iter_start(css, 0, &it);
> > while ((p = css_task_iter_next(&it))) {
> > - for_each_clamp_id(clamp_id) {
> > - if ((0x1 << clamp_id) & clamps)
> > - uclamp_update_active(p, clamp_id);
> > - }
> > + for_each_clamp_id(clamp_id)
> > + uclamp_update_active(p, clamp_id);
> > }
> > css_task_iter_end(&it);
> > }
> > @@ -9626,7 +9613,7 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css)
> > }
> >
> > /* Immediately update descendants RUNNABLE tasks */
> > - uclamp_update_active_tasks(css, clamps);
> > + uclamp_update_active_tasks(css);
>
> Since we now always have to update both clamp_id's, can you not update
> both under the same task_rq_lock() (in uclamp_update_active())?
Good idea. Done this
--->8---
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b4e856a4335d..fdb9a109fd68 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1620,8 +1620,9 @@ static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
}
static inline void
-uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
+uclamp_update_active(struct task_struct *p)
{
+ enum uclamp_id clamp_id;
struct rq_flags rf;
struct rq *rq;
@@ -1641,9 +1642,11 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
* affecting a valid clamp bucket, the next time it's enqueued,
* it will already see the updated clamp bucket value.
*/
- if (p->uclamp[clamp_id].active) {
- uclamp_rq_dec_id(rq, p, clamp_id);
- uclamp_rq_inc_id(rq, p, clamp_id);
+ for_each_clamp_id(clamp_id) {
+ if (p->uclamp[clamp_id].active) {
+ uclamp_rq_dec_id(rq, p, clamp_id);
+ uclamp_rq_inc_id(rq, p, clamp_id);
+ }
}
task_rq_unlock(rq, p, &rf);
@@ -1653,15 +1656,12 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
static inline void
uclamp_update_active_tasks(struct cgroup_subsys_state *css)
{
- enum uclamp_id clamp_id;
struct css_task_iter it;
struct task_struct *p;
css_task_iter_start(css, 0, &it);
- while ((p = css_task_iter_next(&it))) {
- for_each_clamp_id(clamp_id)
- uclamp_update_active(p, clamp_id);
- }
+ while ((p = css_task_iter_next(&it)))
+ uclamp_update_active(p);
css_task_iter_end(&it);
}
--->8---
Thanks!
--
Qais Yousef
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