* Russell King <rmk+lkml@xxxxxxxxxxxxxxxx>:
> On Tue, Jul 15, 2008 at 12:16:32PM -0600, Matthew Wilcox wrote:
> > On Tue, Jul 15, 2008 at 11:57:40AM -0600, Alex Chiang wrote:
> > > My thought was that big SMP systems like ia64, possibly sparc and
> > > ppc, and increasingly, x86, might find something like this
> > > useful, as systems get larger and larger, and vendors are going
> > > to want to do RAS-ish features, like the ability to keep CPUs in
> > > firmware across reboots until told otherwise by the sysadmin.
> > >
> > > Right now, a 'present' CPU strongly implies 'online' as well,
> > > since we're calling cpu_up() for all 'present' CPUs in
> > > smp_init(). But this hurts if:
> > >
> > > - you don't actually want to bring up all 'present' CPUs
> > > - you still want to interact with these weirdo zombie
> > > CPUs that are 'present' but not 'online'
> >
> > Have you considered simply failing __cpu_up() for CPUs that are
> > deconfigured by firmware?
>
> But what if you want to have a system boot with, say, 4 CPUs and
> then decide at run time to bring up another 4 CPUs when required?
>
> How about having smp_init() call into arch code to query whether
> it should bring up a not-already-online CPU? Architectures that
> want to do something special can then make the decision there and
> everyone else can define the test completely away.
So this is exactly what I'm doing. The ia64 patch has this hunk:
@@ -820,6 +824,9 @@ __cpu_up (unsigned int cpu)
if (cpu_isset(cpu, cpu_callin_map))
return -EINVAL;
+ if (!cpu_isset(cpu, cpu_enabled_map))
+ return -EINVAL;
+
per_cpu(cpu_state, cpu) = CPU_UP_PREPARE;
/* Processor goes to start_secondary(), sets online flag */
ret = do_boot_cpu(sapicid, cpu);
That was the easiest, most-straightforward solution I could think
of. If you have an idea for a version with lower taxes (doesn't
touch all the archs or can be #define'd out), I'm happy to hear
it.
Thanks.
/ac
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