Re: [ACPI] Re: [RFC 5/6]clean cpu state after hotremove CPU

From: Nathan Lynch (ntl_at_pobox.com)
Date: 04/04/05

  • Next message: David Vrabel: "Re: iomapping a big endian area" 
    Date:	Mon, 4 Apr 2005 10:33:45 -0500
To: Li Shaohua <shaohua.li@intel.com>

    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.

    Nathan
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