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Message-ID: <20070827184939.GA104@tv-sign.ru>
Date: Mon, 27 Aug 2007 22:49:39 +0400
From: Oleg Nesterov <oleg@...sign.ru>
To: Cliff Wickman <cpw@....com>
Cc: akpm@...ux-foundation.org, ego@...ibm.com, mingo@...e.hu,
vatsa@...ibm.com, pj@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] V4: hotplug cpu: migrate a task within its cpuset
On 08/27, Cliff Wickman wrote:
>
> With this patch, migrate the task to:
> 1) to any cpu on the same node as the disabled cpu, which is both online
> and among that task's cpus_allowed
> 2) to any online cpu within the task's cpuset
> 3) to any cpu which is both online and among that task's cpus_allowed
I think the patch is correct.
Actually, it looks like "bugfix: fix cpu-hotplug with cpusets interaction" to me.
Not only we migrate to the "right" CPU (accoridng to 2), we also try to preserve
the correct ->cpus_allowed to stay within our ->cpuset.
(if only I really understood what cpuset is :)
Oleg.
> include/linux/cpuset.h | 5 +++++
> kernel/cpuset.c | 15 ++++++++++++++-
> kernel/sched.c | 13 ++++++++++++-
> 3 files changed, 31 insertions(+), 2 deletions(-)
>
> Index: linus.070821/kernel/sched.c
> ===================================================================
> --- linus.070821.orig/kernel/sched.c
> +++ linus.070821/kernel/sched.c
> @@ -61,6 +61,7 @@
> #include <linux/delayacct.h>
> #include <linux/reciprocal_div.h>
> #include <linux/unistd.h>
> +#include <linux/cpuset.h>
>
> #include <asm/tlb.h>
>
> @@ -5093,8 +5094,16 @@ restart:
>
> /* No more Mr. Nice Guy. */
> if (dest_cpu == NR_CPUS) {
> + cpumask_t cpus_allowed = cpuset_cpus_allowed_locked();
> + /*
> + * Try to stay on the same cpuset, where the current cpuset
> + * may be a subset of all cpus.
> + * The cpuset_cpus_allowed_locked() variant of
> + * cpuset_cpus_allowed() will not block
> + * It must be called within calls to cpuset_lock/cpuset_unlock.
> + */
> rq = task_rq_lock(p, &flags);
> - cpus_setall(p->cpus_allowed);
> + p->cpus_allowed = cpus_allowed;
> dest_cpu = any_online_cpu(p->cpus_allowed);
> task_rq_unlock(rq, &flags);
>
> @@ -5412,6 +5421,7 @@ migration_call(struct notifier_block *nf
>
> case CPU_DEAD:
> case CPU_DEAD_FROZEN:
> + cpuset_lock(); /* around calls to cpuset_cpus_allowed_lock() */
> migrate_live_tasks(cpu);
> rq = cpu_rq(cpu);
> kthread_stop(rq->migration_thread);
> @@ -5425,6 +5435,7 @@ migration_call(struct notifier_block *nf
> rq->idle->sched_class = &idle_sched_class;
> migrate_dead_tasks(cpu);
> spin_unlock_irq(&rq->lock);
> + cpuset_unlock();
> migrate_nr_uninterruptible(rq);
> BUG_ON(rq->nr_running != 0);
>
> Index: linus.070821/include/linux/cpuset.h
> ===================================================================
> --- linus.070821.orig/include/linux/cpuset.h
> +++ linus.070821/include/linux/cpuset.h
> @@ -22,6 +22,7 @@ extern void cpuset_init_smp(void);
> extern void cpuset_fork(struct task_struct *p);
> extern void cpuset_exit(struct task_struct *p);
> extern cpumask_t cpuset_cpus_allowed(struct task_struct *p);
> +extern cpumask_t cpuset_cpus_allowed_locked(struct task_struct *p);
> extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
> #define cpuset_current_mems_allowed (current->mems_allowed)
> void cpuset_init_current_mems_allowed(void);
> @@ -87,6 +88,10 @@ static inline cpumask_t cpuset_cpus_allo
> {
> return cpu_possible_map;
> }
> +static inline cpumask_t cpuset_cpus_allowed_locked(struct task_struct *p)
> +{
> + return cpu_possible_map;
> +}
>
> static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
> {
> Index: linus.070821/kernel/cpuset.c
> ===================================================================
> --- linus.070821.orig/kernel/cpuset.c
> +++ linus.070821/kernel/cpuset.c
> @@ -2325,10 +2325,23 @@ cpumask_t cpuset_cpus_allowed(struct tas
> cpumask_t mask;
>
> mutex_lock(&callback_mutex);
> + mask = cpuset_cpus_allowed_locked(tsk);
> + mutex_unlock(&callback_mutex);
> +
> + return mask;
> +}
> +
> +/**
> + * cpuset_cpus_allowed_locked - return cpus_allowed mask from a tasks cpuset.
> + * Must be called with callback_mutex held.
> + **/
> +cpumask_t cpuset_cpus_allowed_locked(struct task_struct *tsk)
> +{
> + cpumask_t mask;
> +
> task_lock(tsk);
> guarantee_online_cpus(tsk->cpuset, &mask);
> task_unlock(tsk);
> - mutex_unlock(&callback_mutex);
>
> return mask;
> }
-
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