Messages in this thread | | | Date | Tue, 22 Jul 2008 12:19:00 -0400 | From | Gautham R Shenoy <> | Subject | Re: + pm-introduce-new-interfaces-schedule_work_on-and-queue_work_on.patch added to -mm tree |
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On Sat, Jul 12, 2008 at 08:21:49PM +0400, Oleg Nesterov wrote: > (Gautham cc'ed) >
Sorry for the delay... I'm a bit tied down to other things until aug 20th :(
> On 07/11, Andrew Morton wrote: > > > > Subject: pm: introduce new interfaces schedule_work_on() and queue_work_on() > > From: Zhang Rui <rui.zhang@intel.com> > > > > This interface allows adding a job on a specific cpu. > > > > Although a work struct on a cpu will be scheduled to other cpu if the cpu > > dies, there is a recursion if a work task tries to offline the cpu it's > > running on. we need to schedule the task to a specific cpu in this case. > > http://bugzilla.kernel.org/show_bug.cgi?id=10897 > > So, this is used in http://bugzilla.kernel.org/attachment.cgi?id=16707 > > --- linux-2.6.orig/kernel/power/poweroff.c 2008-06-30 16:01:35.000000000 +0800 > +++ linux-2.6/kernel/power/poweroff.c 2008-07-03 10:50:05.000000000 +0800 > @@ -25,7 +25,8 @@ > > static void handle_poweroff(int key, struct tty_struct *tty) > { > - schedule_work(&poweroff_work); > + /* run sysrq poweroff on boot cpu */ > + schedule_work_on(first_cpu(cpu_online_map), &poweroff_work); > } > > static struct sysrq_key_op sysrq_poweroff_op = { > > A couple of silly questions, I don't understand the low-level details. > > This patch (and kernel_power_off() afaics) assumes that the boot cpu > can't be cpu_down()'ed. Is it true in general? For example, grep shows > that arch/s390/kernel/smp.c:topology_init()->smp_add_present_cpu() > sets ->hotpluggable = 1 for all present CPUs?
I tried this on a Power system sometime back and I was able to offline CPU0. What I am not sure however, is if that was the boot-cpu.
On x86, I do remember reading somewhere why we cannot offline CPU0.
/me searches.
Yes, in arch/x86/kernel/topology.c
int __ref arch_register_cpu(int num) { /* * CPU0 cannot be offlined due to several * restrictions and assumptions in kernel. This basically * doesnt add a control file, one cannot attempt to offline * BSP. * * Also certain PCI quirks require not to enable hotplug control * for all CPU's. */ if (num) per_cpu(cpu_devices, num).cpu.hotpluggable = 1; return register_cpu(&per_cpu(cpu_devices, num).cpu, num); }
> > Another question. I can't understand why first_cpu(cpu_online_map) is > always the boot CPU on every arch. IOW, shouldn't boot_cpu_init() set > some "boot_cpu = smp_processor_id()" which should be use instead of > first_cpu(cpu_online_map) ? >
Not very sure about this one. > Thanks, > > Oleg. >
-- Thanks and Regards gautham
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