• Michael Ellerman's avatar
    powerpc/powernv: Add support for POWER8 split core on powernv · e2186023
    Michael Ellerman authored
    Upcoming POWER8 chips support a concept called split core. This is where the
    core can be split into subcores that although not full cores, are able to
    appear as full cores to a guest.
    
    The splitting & unsplitting procedure is mildly complicated, and explained at
    length in the comments within the patch.
    
    One notable detail is that when splitting or unsplitting we need to pull
    offline cpus out of their offline state to do work as part of the procedure.
    
    The interface for changing the split mode is via a sysfs file, eg:
    
     $ echo 2 > /sys/devices/system/cpu/subcores_per_core
    
    Currently supported values are '1', '2' and '4'. And indicate respectively that
    the core should be unsplit, split in half, and split in quarters. These modes
    correspond to threads_per_subcore of 8, 4 and 2.
    
    We do not allow changing the split mode while KVM VMs are active. This is to
    prevent the value changing while userspace is configuring the VM, and also to
    prevent the mode being changed in such a way that existing guests are unable to
    be run.
    
    CPU hotplug fixes by Srivatsa.  max_cpus fixes by Mahesh.  cpuset fixes by
    benh.  Fix for irq race by paulus.  The rest by mikey and mpe.
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: default avatarMichael Neuling <mikey@neuling.org>
    Signed-off-by: default avatarSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    Signed-off-by: default avatarMahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
    Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
    e2186023
powernv.h 610 Bytes