* 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. I experimented today with an ia64-only solution, keeping track of 'present' vs 'enabled' vs 'online' all in arch-specific code. The arch-specific stuff turns out to be more or less a wash; that is, it's not too hard to keep it all in ia64. However, the problem is, I would still need a generic 'enabled_map' to control whether 'online' and 'crash_notes' entries get created for /sys/devices/system/cpu/cpuN/. So if other archs are at least neutral on this class of CPUs, I can work on another patchset that lowers the tax to a simple #define for archs that don't care. But if people hate this idea of a new map, I'd like to know so that I'm not wasting my time and can work on a different solution (what that would be, I have no idea at the moment). Thanks. /ac -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
