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Date: Mon, 6 May 2024 16:04:22 +0800
From: Xuewen Yan <xuewen.yan94@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Xuewen Yan <xuewen.yan@...soc.com>, akpm@...ux-foundation.org, oleg@...hat.com,
longman@...hat.com, dylanbhatch@...gle.com, rick.p.edgecombe@...el.com,
ke.wang@...soc.com, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] sched/proc: Print user_cpus_ptr for task status
Hi Peter
On Mon, Apr 29, 2024 at 8:10 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Mon, Apr 29, 2024 at 04:46:33PM +0800, Xuewen Yan wrote:
> > The commit 851a723e45d1c("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()")
> > would clear the user_cpus_ptr when call the do_set_cpus_allowed.
> >
> > In order to determine whether the user_cpus_ptr is taking effect,
> > it is better to print the task's user_cpus_ptr.
>
> This is an ABI change and would mandate we forever more have this
> distinction. I don't think your changes justifies things sufficiently
> for this.
I added this mainly because online/offline cpu will produce different
results for the !top-cpuset task.
For example:
If the task was running, then offline task's cpus, would lead to clear
its user-mask.
unisoc:/ # while true; do sleep 600; done&
[1] 6786
unisoc:/ # echo 6786 > /dev/cpuset/top-app/tasks
unisoc:/ # cat /dev/cpuset/top-app/cpus
0-7
unisoc:/ # cat /proc/6786/status | grep Cpus
Cpus_allowed: ff
Cpus_allowed_list: 0-7
Cpus_user_allowed: (null)
Cpus_user_allowed_list: (null)
unisoc:/ # taskset -p c0 6786
pid 6786's current affinity mask: ff
pid 6786's new affinity mask: c0
unisoc:/ # cat /proc/6786/status | grep Cpus
Cpus_allowed: c0
Cpus_allowed_list: 6-7
Cpus_user_allowed: c0
Cpus_user_allowed_list: 6-7
After offline the cpu6 and cpu7, the user-mask would be cleared:
unisoc:/ # echo 0 > /sys/devices/system/cpu/cpu7/online
unisoc:/ # cat /proc/6786/status | grep Cpus
Cpus_allowed: 40
Cpus_allowed_list: 6
Cpus_user_allowed: c0
Cpus_user_allowed_list: 6-7
ums9621_1h10:/ # echo 0 > /sys/devices/system/cpu/cpu6/online
ums9621_1h10:/ # cat /proc/6786/status | grep Cpus
Cpus_allowed: 3f
Cpus_allowed_list: 0-5
Cpus_user_allowed: (null)
Cpus_user_allowed_list: (null)
When online the cpu6/7, the user-mask can not bring back:
unisoc:/ # echo 1 > /sys/devices/system/cpu/cpu6/online
unisoc:/ # cat /proc/6786/status | grep Cpus
Cpus_allowed: 7f
Cpus_allowed_list: 0-6
Cpus_user_allowed: (null)
Cpus_user_allowed_list: (null)
unisoc:/ # echo 1 > /sys/devices/system/cpu/cpu7/online
unisoc:/ # cat /proc/6786/status | grep Cpus
Cpus_allowed: ff
Cpus_allowed_list: 0-7
Cpus_user_allowed: (null)
Cpus_user_allowed_list: (null)
However, if we offline the cpu when the task is sleeping, at this
time, because would not call the fallback_cpu(), its user-mask will
not be cleared.
unisoc:/ # while true; do sleep 600; done&
[1] 5990
unisoc:/ # echo 5990 > /dev/cpuset/top-app/tasks
unisoc:/ # cat /proc/5990/status | grep Cpus
Cpus_allowed: ff
Cpus_allowed_list: 0-7
Cpus_user_allowed: (null)
Cpus_user_allowed_list: (null)
unisoc:/ # taskset -p c0 5990
pid 5990's current affinity mask: ff
pid 5990's new affinity mask: c0
unisoc:/ # cat /proc/5990/status | grep Cpus
Cpus_allowed: c0
Cpus_allowed_list: 6-7
Cpus_user_allowed: c0
Cpus_user_allowed_list: 6-7
unisoc:/ # echo 0 > /sys/devices/system/cpu/cpu6/online
unisoc:/ # cat /proc/5990/status | grep Cpus
Cpus_allowed: 80
Cpus_allowed_list: 7
Cpus_user_allowed: c0
Cpus_user_allowed_list: 6-7
unisoc:/ # echo 0 > /sys/devices/system/cpu/cpu7/online
unisoc:/ # cat /proc/5990/status | grep Cpus
Cpus_allowed: 3f
Cpus_allowed_list: 0-5
Cpus_user_allowed: c0
Cpus_user_allowed_list: 6-7
After 10 minutes, it was waked up, it can also keep its user-mask:
ums9621_1h10:/ # cat /proc/5990/status | grep Cpus
Cpus_allowed: 3f
Cpus_allowed_list: 0-5
Cpus_user_allowed: c0
Cpus_user_allowed_list: 6-7
In order to solve the above problem, I modified the following patch.
At this time, for !top-cpuset, regardless of whether the task is in
the running state when offline cpu, its cpu-mask can be maintained.
However, this patch may not be perfect yet, so I send the "Print
user_cpus_ptr for task status" patch first to debug more conveniently.
--->
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 68cfa656b9b1..00879b6de8d4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1870,7 +1870,7 @@ extern void dl_bw_free(int cpu, u64 dl_bw);
#ifdef CONFIG_SMP
/* do_set_cpus_allowed() - consider using set_cpus_allowed_ptr() instead */
-extern void do_set_cpus_allowed(struct task_struct *p, const struct
cpumask *new_mask);
+extern void do_set_cpus_allowed(struct task_struct *p, const struct
cpumask *new_mask, bool keep_user);
/**
* set_cpus_allowed_ptr - set CPU affinity mask of a task
@@ -1886,7 +1886,7 @@ extern int dl_task_check_affinity(struct
task_struct *p, const struct cpumask *m
extern void force_compatible_cpus_allowed_ptr(struct task_struct *p);
extern void relax_compatible_cpus_allowed_ptr(struct task_struct *p);
#else
-static inline void do_set_cpus_allowed(struct task_struct *p, const
struct cpumask *new_mask)
+static inline void do_set_cpus_allowed(struct task_struct *p, const
struct cpumask *new_mask, bool keep_user)
{
}
static inline int set_cpus_allowed_ptr(struct task_struct *p, const
struct cpumask *new_mask)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 7ee9994aee40..0c448f8a3829 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -4005,9 +4005,14 @@ bool cpuset_cpus_allowed_fallback(struct
task_struct *tsk)
rcu_read_lock();
cs_mask = task_cs(tsk)->cpus_allowed;
- if (is_in_v2_mode() && cpumask_subset(cs_mask, possible_mask)) {
- do_set_cpus_allowed(tsk, cs_mask);
- changed = true;
+ if (cpumask_subset(cs_mask, possible_mask)) {
+ if (is_in_v2_mode()) {
+ do_set_cpus_allowed(tsk, cs_mask, false);
+ changed = true;
+ } else if (task_cs(tsk) != &top_cpuset) {
+ do_set_cpus_allowed(tsk, cs_mask, true);
+ changed = true;
+ }
}
rcu_read_unlock();
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 7a7aa5f93c0c..7ede27630088 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -527,7 +527,7 @@ static void __kthread_bind_mask(struct task_struct
*p, const struct cpumask *mas
/* It's safe because the task is inactive. */
raw_spin_lock_irqsave(&p->pi_lock, flags);
- do_set_cpus_allowed(p, mask);
+ do_set_cpus_allowed(p, mask, false);
p->flags |= PF_NO_SETAFFINITY;
raw_spin_unlock_irqrestore(&p->pi_lock, flags);
}
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 33cfd522fc7c..623f89e65e6c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2855,18 +2855,21 @@ __do_set_cpus_allowed(struct task_struct *p,
struct affinity_context *ctx)
* Used for kthread_bind() and select_fallback_rq(), in both cases the user
* affinity (if any) should be destroyed too.
*/
-void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
+void do_set_cpus_allowed(struct task_struct *p, const struct cpumask
*new_mask, bool keep_user)
{
struct affinity_context ac = {
.new_mask = new_mask,
.user_mask = NULL,
- .flags = SCA_USER, /* clear the user requested mask */
+ .flags = 0, /* clear the user requested mask */
};
union cpumask_rcuhead {
cpumask_t cpumask;
struct rcu_head rcu;
};
+ if (!keep_user)
+ ac.flags = SCA_USER;
+
__do_set_cpus_allowed(p, &ac);
/*
@@ -2874,7 +2877,8 @@ void do_set_cpus_allowed(struct task_struct *p,
const struct cpumask *new_mask)
* to use kfree() here (when PREEMPT_RT=y), therefore punt to using
* kfree_rcu().
*/
- kfree_rcu((union cpumask_rcuhead *)ac.user_mask, rcu);
+ if (!keep_user)
+ kfree_rcu((union cpumask_rcuhead *)ac.user_mask, rcu);
}
static cpumask_t *alloc_user_cpus_ptr(int node)
@@ -3664,7 +3668,7 @@ int select_fallback_rq(int cpu, struct task_struct *p)
*
* More yuck to audit.
*/
- do_set_cpus_allowed(p, task_cpu_possible_mask(p));
+ do_set_cpus_allowed(p,
task_cpu_possible_mask(p), false);
state = fail;
break;
case fail:
---
xuewen
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