• Paul Mackerras's avatar
    KVM: PPC: Book3S HV: Make use of unused threads when running guests · ec257165
    Paul Mackerras authored
    When running a virtual core of a guest that is configured with fewer
    threads per core than the physical cores have, the extra physical
    threads are currently unused.  This makes it possible to use them to
    run one or more other virtual cores from the same guest when certain
    conditions are met.  This applies on POWER7, and on POWER8 to guests
    with one thread per virtual core.  (It doesn't apply to POWER8 guests
    with multiple threads per vcore because they require a 1-1 virtual to
    physical thread mapping in order to be able to use msgsndp and the
    TIR.)
    
    The idea is that we maintain a list of preempted vcores for each
    physical cpu (i.e. each core, since the host runs single-threaded).
    Then, when a vcore is about to run, it checks to see if there are
    any vcores on the list for its physical cpu that could be
    piggybacked onto this vcore's execution.  If so, those additional
    vcores are put into state VCORE_PIGGYBACK and their runnable VCPU
    threads are started as well as the original vcore, which is called
    the master vcore.
    
    After the vcores have exited the guest, the extra ones are put back
    onto the preempted list if any of their VCPUs are still runnable and
    not idle.
    
    This means that vcpu->arch.ptid is no longer necessarily the same as
    the physical thread that the vcpu runs on.  In order to make it easier
    for code that wants to send an IPI to know which CPU to target, we
    now store that in a new field in struct vcpu_arch, called thread_cpu.
    Reviewed-by: default avatarDavid Gibson <david@gibson.dropbear.id.au>
    Tested-by: default avatarLaurent Vivier <lvivier@redhat.com>
    Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
    Signed-off-by: default avatarAlexander Graf <agraf@suse.de>
    ec257165
kvm_host.h 17.1 KB