Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261286AbVDDFpa (ORCPT ); Mon, 4 Apr 2005 01:45:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261309AbVDDFp3 (ORCPT ); Mon, 4 Apr 2005 01:45:29 -0400 Received: from fmr19.intel.com ([134.134.136.18]:4547 "EHLO orsfmr004.jf.intel.com") by vger.kernel.org with ESMTP id S261286AbVDDFoi (ORCPT ); Mon, 4 Apr 2005 01:44:38 -0400 Subject: Re: [ACPI] Re: [RFC 5/6]clean cpu state after hotremove CPU From: Li Shaohua To: Nathan Lynch Cc: lkml , ACPI-DEV , Zwane Mwaikambo , Len Brown , Pavel Machek In-Reply-To: <20050404052844.GB3611@otto> References: <1112580367.4194.344.camel@sli10-desk.sh.intel.com> <20050404052844.GB3611@otto> Content-Type: text/plain Message-Id: <1112593338.4194.362.camel@sli10-desk.sh.intel.com> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.4.6 (1.4.6-2) Date: Mon, 04 Apr 2005 13:42:18 +0800 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5674 Lines: 180 Hi, On Mon, 2005-04-04 at 13:28, Nathan Lynch wrote: > On Mon, Apr 04, 2005 at 10:07:02AM +0800, Li Shaohua wrote: > > Clean up all CPU states including its runqueue and idle thread, > > so we can use boot time code without any changes. > > Note this makes /sys/devices/system/cpu/cpux/online unworkable. > > In what sense does it make the online attribute unworkable? I removed the idle thread and other CPU states, and makes the dead CPU into a 'halt' busy loop. > > > diff -puN kernel/exit.c~cpu_state_clean kernel/exit.c > > --- linux-2.6.11/kernel/exit.c~cpu_state_clean 2005-03-31 10:50:27.000000000 +0800 > > +++ linux-2.6.11-root/kernel/exit.c 2005-03-31 10:50:27.000000000 +0800 > > @@ -845,6 +845,65 @@ fastcall NORET_TYPE void do_exit(long co > > for (;;) ; > > } > > > > +#ifdef CONFIG_STR_SMP > > +void do_exit_idle(void) > > +{ > > + struct task_struct *tsk = current; > > + int group_dead; > > + > > + BUG_ON(tsk->pid); > > + BUG_ON(tsk->mm); > > + > > + if (tsk->io_context) > > + exit_io_context(); > > + tsk->flags |= PF_EXITING; > > + tsk->it_virt_expires = cputime_zero; > > + tsk->it_prof_expires = cputime_zero; > > + tsk->it_sched_expires = 0; > > + > > + acct_update_integrals(tsk); > > + update_mem_hiwater(tsk); > > + group_dead = atomic_dec_and_test(&tsk->signal->live); > > + if (group_dead) { > > + del_timer_sync(&tsk->signal->real_timer); > > + acct_process(-1); > > + } > > + exit_mm(tsk); > > + > > + exit_sem(tsk); > > + __exit_files(tsk); > > + __exit_fs(tsk); > > + exit_namespace(tsk); > > + exit_thread(); > > + exit_keys(tsk); > > + > > + if (group_dead && tsk->signal->leader) > > + disassociate_ctty(1); > > + > > + module_put(tsk->thread_info->exec_domain->module); > > + if (tsk->binfmt) > > + module_put(tsk->binfmt->module); > > + > > + tsk->exit_code = -1; > > + tsk->exit_state = EXIT_DEAD; > > + > > + /* in release_task */ > > + atomic_dec(&tsk->user->processes); > > + write_lock_irq(&tasklist_lock); > > + __exit_signal(tsk); > > + __exit_sighand(tsk); > > + write_unlock_irq(&tasklist_lock); > > + release_thread(tsk); > > + put_task_struct(tsk); > > + > > + tsk->flags |= PF_DEAD; > > +#ifdef CONFIG_NUMA > > + mpol_free(tsk->mempolicy); > > + tsk->mempolicy = NULL; > > +#endif > > +} > > +#endif > > I don't understand why this is needed at all. It looks like a fair > amount of code from do_exit is being duplicated here. Yes, exactly. Someone who understand do_exit please help clean up the code. I'd like to remove the idle thread, since the smpboot code will create a new idle thread. > We've been > doing cpu removal on ppc64 logical partitions for a while and never > needed to do anything like this. Did it remove idle thread? or dead cpu is in a busy loop of idle? > Maybe idle_task_exit would suffice? idle_task_exit seems just drop mm. We need destroy the idle task for physical CPU hotplug, right? > > > > diff -puN kernel/sched.c~cpu_state_clean kernel/sched.c > > --- linux-2.6.11/kernel/sched.c~cpu_state_clean 2005-03-31 10:50:27.000000000 +0800 > > +++ linux-2.6.11-root/kernel/sched.c 2005-04-04 09:06:40.362357104 +0800 > > @@ -4028,6 +4028,58 @@ void __devinit init_idle(task_t *idle, i > > } > > > > /* > > + * Initial dummy domain for early boot and for hotplug cpu. Being static, > > + * it is initialized to zero, so all balancing flags are cleared which is > > + * what we want. > > + */ > > +static struct sched_domain sched_domain_dummy; > > + > > +#ifdef CONFIG_STR_SMP > > +static void __devinit exit_idle(int cpu) > > +{ > > + runqueue_t *rq = cpu_rq(cpu); > > + struct task_struct *p = rq->idle; > > + int j, k; > > + prio_array_t *array; > > + > > + /* init runqueue */ > > + spin_lock_init(&rq->lock); > > + rq->active = rq->arrays; > > + rq->expired = rq->arrays + 1; > > + rq->best_expired_prio = MAX_PRIO; > > + > > + rq->prev_mm = NULL; > > + rq->curr = rq->idle = NULL; > > + rq->expired_timestamp = 0; > > + > > + rq->sd = &sched_domain_dummy; > > + rq->cpu_load = 0; > > + rq->active_balance = 0; > > + rq->push_cpu = 0; > > + rq->migration_thread = NULL; > > + INIT_LIST_HEAD(&rq->migration_queue); > > + atomic_set(&rq->nr_iowait, 0); > > + > > + for (j = 0; j < 2; j++) { > > + array = rq->arrays + j; > > + for (k = 0; k < MAX_PRIO; k++) { > > + INIT_LIST_HEAD(array->queue + k); > > + __clear_bit(k, array->bitmap); > > + } > > + // delimiter for bitsearch > > + __set_bit(MAX_PRIO, array->bitmap); > > + } > > + /* Destroy IDLE thread. > > + * it's safe now, the CPU is in busy loop > > + */ > > + if (p->active_mm) > > + mmdrop(p->active_mm); > > + p->active_mm = NULL; > > + put_task_struct(p); > > +} > > +#endif > > + > > +/* > > * In a system that switches off the HZ timer nohz_cpu_mask > > * indicates which cpus entered this state. This is used > > * in the rcu update to wait only for active cpus. For system > > @@ -4432,6 +4484,9 @@ static int migration_call(struct notifie > > complete(&req->done); > > } > > spin_unlock_irq(&rq->lock); > > +#ifdef CONFIG_STR_SMP > > + exit_idle(cpu); > > +#endif > > I don't understand the need for this, either. The existing cpu > hotplug notifier in the scheduler takes care of initializing the sched > domains and groups appropriately for online/offline events; why do you > need to touch the runqueue structures? If a CPU is physically hotremoved from the system, shouldn't we clean its runqueue? Thanks, Shaohua - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/