Messages in this thread | | | Date | Mon, 4 Apr 2005 10:33:45 -0500 | From | Nathan Lynch <> | Subject | Re: [ACPI] Re: [RFC 5/6]clean cpu state after hotremove CPU |
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On Mon, Apr 04, 2005 at 01:42:18PM +0800, Li Shaohua wrote: > 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.
I'd say fix the smpboot code so that it doesn't create new idle tasks except during boot.
> > > 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?
Neither. The cpu is definitely offline, but there is no reason to free the idle thread.
> > > Maybe idle_task_exit would suffice? > idle_task_exit seems just drop mm. We need destroy the idle task for > physical CPU hotplug, right?
No.
> > > > 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?
No. It should make zero difference to the scheduler whether the "play dead" cpu hotplug or "physical" hotplug is being used.
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