• Gautham R Shenoy's avatar
    powerpc/pseries: Add hooks to put the CPU into an appropriate offline state · 3aa565f5
    Gautham R Shenoy authored
    When a CPU is offlined on POWER currently, we call rtas_stop_self() and hand
    the CPU back to the resource pool. This path is used for DLPAR which will
    cause a change in the LPAR configuration which will be visible outside.
    
    This patch changes the default state a CPU is put into when it is offlined.
    On platforms which support ceding the processor to the hypervisor with
    latency hint specifier value, during a cpu offline operation,
    instead of calling rtas_stop_self(), we cede the vCPU to the hypervisor
    while passing a latency hint specifier value. The Hypervisor can use this hint
    to provide better energy savings. Also, during the offline
    operation, the control of the vCPU remains with the LPAR as oppposed to
    returning it to the resource pool.
    
    The patch achieves this by creating an infrastructure to set the
    preferred_offline_state() which can be either
    - CPU_STATE_OFFLINE: which is the current behaviour of calling
      rtas_stop_self()
    
    - CPU_STATE_INACTIVE: which cedes the vCPU to the hypervisor with the latency
      hint specifier.
    
    The codepath which wants to perform a DLPAR operation can set the
    preferred_offline_state() of a CPU to CPU_STATE_OFFLINE before invoking
    cpu_down().
    
    The patch also provides a boot-time command line argument to disable/enable
    CPU_STATE_INACTIVE.
    Signed-off-by: default avatarGautham R Shenoy <ego@in.ibm.com>
    Signed-off-by: default avatarNathan Fontenot <nfont@austin.ibm.com>
    Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
    3aa565f5
hotplug-cpu.c 11.6 KB