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Message-Id: <20210617165155.3774110-1-qais.yousef@arm.com>
Date: Thu, 17 Jun 2021 17:51:55 +0100
From: Qais Yousef <qais.yousef@....com>
To: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>
Cc: Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
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, Qais Yousef <qais.yousef@....com>
Subject: [PATCH v2] sched/uclamp: Fix uclamp_tg_restrict()
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
inversion between uclamp requested by task (p) and the uclamp values of
the taskgroup it's attached to (tg). Following table demonstrates
2 corner cases:
| p | tg | effective
-----------+-----+------+-----------
CASE 1
-----------+-----+------+-----------
uclamp_min | 60% | 0% | 60%
-----------+-----+------+-----------
uclamp_max | 80% | 50% | 50%
-----------+-----+------+-----------
CASE 2
-----------+-----+------+-----------
uclamp_min | 0% | 30% | 30%
-----------+-----+------+-----------
uclamp_max | 20% | 50% | 20%
-----------+-----+------+-----------
With this fix we get:
| p | tg | effective
-----------+-----+------+-----------
CASE 1
-----------+-----+------+-----------
uclamp_min | 60% | 0% | 50%
-----------+-----+------+-----------
uclamp_max | 80% | 50% | 50%
-----------+-----+------+-----------
CASE 2
-----------+-----+------+-----------
uclamp_min | 0% | 30% | 30%
-----------+-----+------+-----------
uclamp_max | 20% | 50% | 30%
-----------+-----+------+-----------
Additionally uclamp_update_active_tasks() must now unconditionally
update both UCLAMP_MIN/MAX because changing the tg's UCLAMP_MAX for
instance could have an impact on the effective UCLAMP_MIN of the tasks.
| p | tg | effective
-----------+-----+------+-----------
old
-----------+-----+------+-----------
uclamp_min | 60% | 0% | 50%
-----------+-----+------+-----------
uclamp_max | 80% | 50% | 50%
-----------+-----+------+-----------
*new*
-----------+-----+------+-----------
uclamp_min | 60% | 0% | *60%*
-----------+-----+------+-----------
uclamp_max | 80% |*70%* | *70%*
-----------+-----+------+-----------
[1] https://lore.kernel.org/lkml/CAB8ipk_a6VFNjiEnHRHkUMBKbA+qzPQvhtNjJ_YNzQhqV_o8Zw@mail.gmail.com/
Reported-by: Xuewen Yan <xuewen.yan94@...il.com>
Fixes: 0c18f2ecfcc2 ("sched/uclamp: Fix wrong implementation of cpu.uclamp.min")
Signed-off-by: Qais Yousef <qais.yousef@....com>
---
Changes in v2:
* Fixed a typo in commit message (Diemtar).
* Renamed uc_eff back to uc_req (Dietmar).
* Move the loop to update clamp_id to be done once inside the
task_rq_lock() (Dietmar).
kernel/sched/core.c | 49 +++++++++++++++++----------------------------
1 file changed, 18 insertions(+), 31 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9e9a5be35cde..fdb9a109fd68 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1403,8 +1403,10 @@ 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)
{
+ /* Copy by value as we could modify it */
struct uclamp_se uc_req = 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
@@ -1415,23 +1417,11 @@ uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
if (task_group(p) == &root_task_group)
return uc_req;
- 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_req.value;
+ value = clamp(value, tg_min, tg_max);
+ uclamp_se_set(&uc_req, value, false);
#endif
return uc_req;
@@ -1630,8 +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;
@@ -1651,9 +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);
@@ -1661,20 +1654,14 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
#ifdef CONFIG_UCLAMP_TASK_GROUP
static inline void
-uclamp_update_active_tasks(struct cgroup_subsys_state *css,
- unsigned int clamps)
+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) {
- if ((0x1 << clamp_id) & clamps)
- uclamp_update_active(p, clamp_id);
- }
- }
+ while ((p = css_task_iter_next(&it)))
+ uclamp_update_active(p);
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);
}
}
--
2.25.1
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