Am 17.09.2011 um 18:58 schrieb Blue Swirl <blauwir...@gmail.com>: > On Wed, Sep 14, 2011 at 8:42 AM, Alexander Graf <ag...@suse.de> wrote: >> CPUs that are not the boot CPU need to run in spinning code to check if they >> should run off to execute and if so where to jump to. This usually happens >> by leaving secondary CPUs looping and checking if some variable in memory >> changed. >> >> In an environment like Qemu however we can be more clever. We can just export >> the spin table the primary CPU modifies as MMIO region that would event based >> wake up the respective secondary CPUs. That saves us quite some cycles while >> the secondary CPUs are not up yet. >> >> So this patch adds a PV device that simply exports the spinning table into >> the >> guest and thus allows the primary CPU to wake up secondary ones. > > On Sparc32, there is no need for a PV device. The CPU is woken up from > halted state with an IPI. Maybe you could use this approach?
The way it's done here is defined by u-boot and now also nailed down in the ePAPR architecture spec. While alternatives might be more appealing, this is how guests work today :). Alex >
