Messages in this thread | | | Date | Tue, 15 Jul 2008 13:15:15 -0600 | From | Alex Chiang <> | Subject | Re: [PATCH 01/14] Introduce cpu_enabled_map and friends |
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* Russell King <rmk+lkml@arm.linux.org.uk>: > 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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