• Paul Mackerras's avatar
    KVM: PPC: Book3S HV: Allow for running POWER9 host in single-threaded mode · 516f7898
    Paul Mackerras authored
    This patch allows for a mode on POWER9 hosts where we control all the
    threads of a core, much as we do on POWER8.  The mode is controlled by
    a module parameter on the kvm_hv module, called "indep_threads_mode".
    The normal mode on POWER9 is the "independent threads" mode, with
    indep_threads_mode=Y, where the host is in SMT4 mode (or in fact any
    desired SMT mode) and each thread independently enters and exits from
    KVM guests without reference to what other threads in the core are
    doing.
    
    If indep_threads_mode is set to N at the point when a VM is started,
    KVM will expect every core that the guest runs on to be in single
    threaded mode (that is, threads 1, 2 and 3 offline), and will set the
    flag that prevents secondary threads from coming online.  We can still
    use all four threads; the code that implements dynamic micro-threading
    on POWER8 will become active in over-commit situations and will allow
    up to three other VCPUs to be run on the secondary threads of the core
    whenever a VCPU is run.
    
    The reason for wanting this mode is that this will allow us to run HPT
    guests on a radix host on a POWER9 machine that does not support
    "mixed mode", that is, having some threads in a core be in HPT mode
    while other threads are in radix mode.  It will also make it possible
    to implement a "strict threads" mode in future, if desired.
    Signed-off-by: default avatarPaul Mackerras <paulus@ozlabs.org>
    516f7898
kvm_host.h 19.8 KB