On Tue, Jul 15, 2008 at 01:15:15PM -0600, Alex Chiang wrote: > * 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. I think I did make a suggestion in the bit you quote from me above. Let me be more explicit: static void __init smp_init(void) { unsigned int cpu; /* FIXME: This should be done in userspace --RR */ for_each_present_cpu(cpu) { if (num_online_cpus() >= setup_max_cpus) break; - if (!cpu_online(cpu)) + if (smp_cpu_enabled(cpu) && !cpu_online(cpu)) cpu_up(cpu); } /* Any cleanup work */ printk(KERN_INFO "Brought up %ld CPUs\n", (long)num_online_cpus()); smp_cpus_done(setup_max_cpus); } and have architectures provide 'smp_cpu_enabled(cpu)' which can either be a function, inline function or a macro (and therefore possible to be completely eliminated.) -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html