On Fri, 23 Jun 2006 10:50:58 +0900 KAMEZAWA Hiroyuki wrote:
> Hi,
> thank you for good responses. This is avoid_cpu_removal_if_busy patch.
>
> I added all folks to CC who replied previous "stop_on_cpu_lost" discussion.
>
> How about this ?
> (my vocabulary is not rich, then please tell me if you know better name for
> sysctl.)
>
> Changes from old version
> - added sysctl
>
> -Kame
> ==
>
> Now, cpu hot remove migrates all tasks on target cpu by force.
>
> During cpu-hot-remove, if tsk->cpus_allowed contains the only target
> cpu of removal, tsk->cpus_allowd is disposed and the kernel migrate it to
> random cpu.It's obvious that user-land configuration before cpu hot removal
> is bad. But this is not good in carefully scheduled environment.
>
> In this case,
> 1. ignore bad configuration in user-land just do warnings.
> 2. cancel cpu hot removal and warn users to fix the problem and retry.
> seems to be a realisitc workaround. Killing the problematic process may
> cause some trouble in user-land (dead-lock etc..)
>
> This patch adds sysctl moderate_cpu_removal.
> If moderate_cpu_removal == 0, all tasks are migrated by force.
> If moderate_cpu_removal == 1, cpu_hotremoval can fail because of not-
> migratable tasks.
Maybe cpu_removal_migrate? I think that inverts the sysctl
values though, like so:
If cpu_removal_migrate == 1, all tasks are migrated by force.
If cpu_removal_migrate == 0, cpu_hotremoval can fail because of
not-migratable tasks (tasks bound to the target CPU).
and init. the sysctl value to 1 as default.
> Signed-Off-By: KAMEZAWA Hiroyuki <[email protected]>
>
>
>
> include/linux/sysctl.h | 1 +
> kernel/sched.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> kernel/sysctl.c | 13 +++++++++++++
> 3 files changed, 56 insertions(+)
>
> Index: linux-2.6.17.org/kernel/sched.c
> ===================================================================
> --- linux-2.6.17.org.orig/kernel/sched.c
> +++ linux-2.6.17.org/kernel/sched.c
> @@ -4562,6 +4562,44 @@ wait_to_die:
> }
>
> #ifdef CONFIG_HOTPLUG_CPU
> +/*
> + * if moderate_cpu_removal==1 (sysctl), cpu-hot-remove will fail if cpu is busy.
> + * Default value is 0. all tasks are forced to migrate.
> + */
> +int moderate_cpu_removal;
This is also declared (defined? I get those mixed up) in
kernel/sysctl.c. One of them (this one I think) should be
extern, but we prefer externs in a header file if possible.
> +
> +/*
> + * test there are tasks tightly coupled to the target cpu.
> + */
> +static int test_cpu_busy(int cpu)
> +{
> + cpumask_t mask;
> + int ret = 0;
> + pid_t pid;
> + struct task_struct *p;
> + cpus_clear(mask);
> + cpu_set(cpu, mask);
> +
> + read_lock(&tasklist_lock);
> + for_each_process(p) {
> + if (p == current)
> + continue;
> + if (p->mm && cpus_equal(mask, p->cpus_allowed)) {
> + ret = 1;
> + pid = p->pid;
> + break;
> + }
> + }
> + read_unlock(&tasklist_lock);
> + if (ret) {
> + printk(KERN_ERR "cpu(%d) is busy because of task(%d)\n",
> + cpu, pid);
> + printk(KERN_ERR "adjust task(%d) configuration or set "
> + "moderate_cpu_removal to 0 to remove cpu %d\n",
> + pid, cpu);
> + }
> + return ret;
> +}
> /* Figure out where task on dead CPU should go, use force if neccessary. */
> static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *tsk)
> {
> @@ -4752,6 +4790,10 @@ static int migration_call(struct notifie
> kthread_stop(cpu_rq(cpu)->migration_thread);
> cpu_rq(cpu)->migration_thread = NULL;
> break;
> + case CPU_DOWN_PREPARE:
> + if (moderate_cpu_removal && test_cpu_bust(cpu))
> + return NOTIFY_BAD;
> + break;
> case CPU_DEAD:
> migrate_live_tasks(cpu);
> rq = cpu_rq(cpu);
> Index: linux-2.6.17.org/kernel/sysctl.c
> ===================================================================
> --- linux-2.6.17.org.orig/kernel/sysctl.c
> +++ linux-2.6.17.org/kernel/sysctl.c
> @@ -78,6 +78,9 @@ int unknown_nmi_panic;
> extern int proc_unknown_nmi_panic(ctl_table *, int, struct file *,
> void __user *, size_t *, loff_t *);
> #endif
> +#ifdef CONFIG_HOTPLUG_CPU
> +int moderate_cpu_removal;
> +#endif
>
> /* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
> static int maxolduid = 65535;
> @@ -683,6 +686,16 @@ static ctl_table kern_table[] = {
> .proc_handler = &proc_dointvec,
> },
> #endif
> +#ifdef CONFIG_HOTPLUG_CPU
> + {
> + .ctl_name = KERN_MODERATE_CPU_REMOVAL,
> + .procname = "moderate_cpu_removal",
> + .data = &moderate_cpu_removal,
> + .maxlen = sizeof(int),
> + .mode = 0644,
> + .proc_handler = &proc_dointvec,
> + }
> +#endif
> { .ctl_name = 0 }
> };
>
> Index: linux-2.6.17.org/include/linux/sysctl.h
> ===================================================================
> --- linux-2.6.17.org.orig/include/linux/sysctl.h
> +++ linux-2.6.17.org/include/linux/sysctl.h
> @@ -148,6 +148,7 @@ enum
> KERN_SPIN_RETRY=70, /* int: number of spinlock retries */
> KERN_ACPI_VIDEO_FLAGS=71, /* int: flags for setting up video after ACPI sleep */
> KERN_IA64_UNALIGNED=72, /* int: ia64 unaligned userland trap enable */
> + KERN_MODERATE_CPU_REMOVAL=73, /* int: disallow forced cpu removal */
> };
---
~Randy
-
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