On Monday, 16 April 2007 09:05, Pavel Machek wrote:
> Hi!
>
> > As I said before, we have a problem with using the CPU hotplug for suspending
> > because of the notifiers that are called from within cpu_up()/cpu_down() and
> > (sometimes) assume that the system is fully functional.
> >
> > One obvious solution of this problem would be to make the notifiers behave
> > differently if tasks are frozen, but for this purpose we'd need to tell them
> > that this is the case. In principle, we could do it in many different ways
> > (eg. by using a global variable, with the help of suspend notifiers etc.), but
> > IMO one of the cleanest methods woud be to use some special values for the
> > notifications occuring while tasks are frozen (eg. CPU_DEAD_FROZEN instead of
> > CPU_DEAD etc.). In that case the notifiers could react in some special ways
> > to the "FROZEN" notfifications and that would allow us to simplify some code
> > paths (eg. in the microcode driver).
> >
> > The appended patch introduces such "FROZEN" notfifications, modifies the CPU
> > hotplug core to use them and updates all of the users of CPU hotplug notifiers
> > to recognize them. For now, they are treated in the same way as the
> > corresponding "normal" notifications, but I'm going to modify the microcode
> > driver to really use them and I believe that some other subsystems can benefit
> > from using them as well.
> >
> > The patch is totally experimental and untested, although it's been successfully
> > compiled on x86_64 and it's main purpose is to show what exactly I
> > mean. :-)
>
> Looks sane to me.
>
> > Index: linux-2.6.21-rc6/kernel/cpu.c
> > ===================================================================
> > --- linux-2.6.21-rc6.orig/kernel/cpu.c 2007-04-16 00:24:56.000000000 +0200
> > +++ linux-2.6.21-rc6/kernel/cpu.c 2007-04-16 00:25:14.000000000 +0200
> > @@ -120,11 +120,12 @@ static int take_cpu_down(void *unused)
> > }
> >
> > /* Requires cpu_add_remove_lock to be held */
> > -static int _cpu_down(unsigned int cpu)
> > +static int _cpu_down(unsigned int cpu, int tasks_frozen)
> > {
> > int err;
> > struct task_struct *p;
> > cpumask_t old_allowed, tmp;
> > + unsigned long mod = tasks_frozen ? 0x0008 : 0;
> >
>
> Can we get constant instead of 0x0008 here?
Sure. Updated patch is in the reply to Gautham.
Greetings,
Rafael
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