Messages in this thread | | | Date | Mon, 8 Mar 2010 20:37:37 +0100 | From | Heiko Carstens <> | Subject | Re: [PATCH 2/4] stop_machine: reimplement using cpuhog |
| |
On Mon, Mar 08, 2010 at 07:27:08PM +0100, Oleg Nesterov wrote: > On 03/08, Heiko Carstens wrote: > > > > On Tue, Mar 09, 2010 at 12:53:21AM +0900, Tejun Heo wrote: > > > > > > diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c > > > index 65065ac..afe429e 100644 > > > --- a/arch/s390/kernel/time.c > > > +++ b/arch/s390/kernel/time.c > > > @@ -397,7 +397,6 @@ static void __init time_init_wq(void) > > > if (time_sync_wq) > > > return; > > > time_sync_wq = create_singlethread_workqueue("timesync"); > > > - stop_machine_create(); > > > } > > > > > > /* > > > > The reason we introduced stop_machine_create/destroy was to have a non-failing > > variant that doesn't rely on I/O. > > If we ever see a timesync machine check no I/O will succeed (it blocks) until > > clocks have been synchronized. That means also that we rely on the non-blocking > > semantics that those functions must have that are called via stop_machine. > > This isn't true anymore with the cpu hog infrastructure: > > if passed a blocking function that could wait on I/O we won't see any progress > > anymore and the machine is dead. > > Could you please spell? > > How cpuhog can make a difference? Afaics, we shouldn't pass a blocking callback > to hog_cpus/hog_one_cpu.
Well, it might me true that this shouldn't be done. But I don't see a reason why in general it wouldn't work to pass a function that would block. So it's just a matter of time until somebody uses it for such a purpose. For the current stop_machine implementation it would be broken to pass a blocking function (preemption disabled, interrupts disabled).
| |