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cgroup/cpuset: Reserve DL bandwidth only for root-domain moves

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cpuset_can_attach() currently adds the bandwidth of all migrating
SCHED_DEADLINE tasks to sum_migrate_dl_bw. If the source and destination
cpuset effective CPU masks do not overlap, the whole sum is then
reserved in the destination root domain.

set_cpus_allowed_dl(), however, subtracts bandwidth from the source
root domain only when the affinity change really moves the task between
root domains. A DL task can move between cpusets that are still in the
same root domain, so including that task in sum_migrate_dl_bw can reserve
destination bandwidth without a matching source-side subtraction.

Share the root-domain move test with set_cpus_allowed_dl(). Keep
nr_migrate_dl_tasks counting all migrating deadline tasks for cpuset DL
task accounting, but add to sum_migrate_dl_bw only for tasks that need a
root-domain bandwidth move. Keep using the destination cpuset effective
CPU mask and leave the broader can_attach()/attach() transaction model
unchanged.

Fixes: 2ef269ef1a ("cgroup/cpuset: Free DL BW in case can_attach() fails")
Cc: stable@vger.kernel.org # v6.10+
Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
Reviewed-by: Waiman Long <longman@redhat.com>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Guopeng Zhang
2026-05-09 18:20:31 +08:00
committed by Tejun Heo
parent 4a39eda5fd
commit 5dd74441cb
4 changed files with 39 additions and 19 deletions
Download Patch File Download Diff File Expand all files Collapse all files

9
include/linux/sched/deadline.h
View File

@@ -33,6 +33,15 @@ struct root_domain;
extern void dl_add_task_root_domain(struct task_struct *p);
extern void dl_clear_root_domain(struct root_domain *rd);
extern void dl_clear_root_domain_cpu(int cpu);
/*
* Return whether moving DL task @p to @new_mask requires moving DL
* bandwidth accounting between root domains. This helper is specific to
* DL bandwidth move accounting semantics and is shared by
* cpuset_can_attach() and set_cpus_allowed_dl() so both paths use the
* same source root-domain test.
*/
extern bool dl_task_needs_bw_move(struct task_struct *p,
const struct cpumask *new_mask);
extern u64 dl_cookie;
extern bool dl_bw_visited(int cpu, u64 cookie);

1
kernel/cgroup/cpuset-internal.h
View File

@@ -167,6 +167,7 @@ struct cpuset {
*/
int nr_deadline_tasks;
int nr_migrate_dl_tasks;
/* DL bandwidth that needs destination reservation for this attach. */
u64 sum_migrate_dl_bw;
/*
* CPU used for temporary DL bandwidth allocation during attach;

35
kernel/cgroup/cpuset.c
View File

@@ -2993,7 +2993,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
struct cpuset *cs, *oldcs;
struct task_struct *task;
bool setsched_check;
int ret;
int cpu, ret;
/* used later by cpuset_attach() */
cpuset_attach_old_cs = task_cs(cgroup_taskset_first(tset, &css));
@@ -3038,29 +3038,32 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
}
if (dl_task(task)) {
/*
* Count all migrating DL tasks for cpuset task accounting.
* Only tasks that need a root-domain bandwidth move
* contribute to sum_migrate_dl_bw.
*/
cs->nr_migrate_dl_tasks++;
cs->sum_migrate_dl_bw += task->dl.dl_bw;
if (dl_task_needs_bw_move(task, cs->effective_cpus))
cs->sum_migrate_dl_bw += task->dl.dl_bw;
}
}
if (!cs->nr_migrate_dl_tasks)
if (!cs->sum_migrate_dl_bw)
goto out_success;
if (!cpumask_intersects(oldcs->effective_cpus, cs->effective_cpus)) {
int cpu = cpumask_any_and(cpu_active_mask, cs->effective_cpus);
if (unlikely(cpu >= nr_cpu_ids)) {
ret = -EINVAL;
goto out_unlock;
}
ret = dl_bw_alloc(cpu, cs->sum_migrate_dl_bw);
if (ret)
goto out_unlock;
cs->dl_bw_cpu = cpu;
cpu = cpumask_any_and(cpu_active_mask, cs->effective_cpus);
if (unlikely(cpu >= nr_cpu_ids)) {
ret = -EINVAL;
goto out_unlock;
}
ret = dl_bw_alloc(cpu, cs->sum_migrate_dl_bw);
if (ret)
goto out_unlock;
cs->dl_bw_cpu = cpu;
out_success:
/*
* Mark attach is in progress. This makes validate_change() fail

13
kernel/sched/deadline.c
View File

@@ -3107,20 +3107,18 @@ static void task_woken_dl(struct rq *rq, struct task_struct *p)
static void set_cpus_allowed_dl(struct task_struct *p,
struct affinity_context *ctx)
{
struct root_domain *src_rd;
struct rq *rq;
WARN_ON_ONCE(!dl_task(p));
rq = task_rq(p);
src_rd = rq->rd;
/*
* Migrating a SCHED_DEADLINE task between exclusive
* cpusets (different root_domains) entails a bandwidth
* update. We already made space for us in the destination
* domain (see cpuset_can_attach()).
*/
if (!cpumask_intersects(src_rd->span, ctx->new_mask)) {
if (dl_task_needs_bw_move(p, ctx->new_mask)) {
struct dl_bw *src_dl_b;
src_dl_b = dl_bw_of(cpu_of(rq));
@@ -3137,6 +3135,15 @@ static void set_cpus_allowed_dl(struct task_struct *p,
set_cpus_allowed_common(p, ctx);
}
bool dl_task_needs_bw_move(struct task_struct *p,
const struct cpumask *new_mask)
{
if (!dl_task(p))
return false;
return !cpumask_intersects(task_rq(p)->rd->span, new_mask);
}
/* Assumes rq->lock is held */
static void rq_online_dl(struct rq *rq)
{