• P
    KVM: PPC: Book3S HV: Implement dynamic micro-threading on POWER8 · b4deba5c
    Paul Mackerras 提交于
    This builds on the ability to run more than one vcore on a physical
    core by using the micro-threading (split-core) modes of the POWER8
    chip.  Previously, only vcores from the same VM could be run together,
    and (on POWER8) only if they had just one thread per core.  With the
    ability to split the core on guest entry and unsplit it on guest exit,
    we can run up to 8 vcpu threads from up to 4 different VMs, and we can
    run multiple vcores with 2 or 4 vcpus per vcore.
    
    Dynamic micro-threading is only available if the static configuration
    of the cores is whole-core mode (unsplit), and only on POWER8.
    
    To manage this, we introduce a new kvm_split_mode struct which is
    shared across all of the subcores in the core, with a pointer in the
    paca on each thread.  In addition we extend the core_info struct to
    have information on each subcore.  When deciding whether to add a
    vcore to the set already on the core, we now have two possibilities:
    (a) piggyback the vcore onto an existing subcore, or (b) start a new
    subcore.
    
    Currently, when any vcpu needs to exit the guest and switch to host
    virtual mode, we interrupt all the threads in all subcores and switch
    the core back to whole-core mode.  It may be possible in future to
    allow some of the subcores to keep executing in the guest while
    subcore 0 switches to the host, but that is not implemented in this
    patch.
    
    This adds a module parameter called dynamic_mt_modes which controls
    which micro-threading (split-core) modes the code will consider, as a
    bitmap.  In other words, if it is 0, no micro-threading mode is
    considered; if it is 2, only 2-way micro-threading is considered; if
    it is 4, only 4-way, and if it is 6, both 2-way and 4-way
    micro-threading mode will be considered.  The default is 6.
    
    With this, we now have secondary threads which are the primary thread
    for their subcore and therefore need to do the MMU switch.  These
    threads will need to be started even if they have no vcpu to run, so
    we use the vcore pointer in the PACA rather than the vcpu pointer to
    trigger them.
    
    It is now possible for thread 0 to find that an exit has been
    requested before it gets to switch the subcore state to the guest.  In
    that case we haven't added the guest's timebase offset to the
    timebase, so we need to be careful not to subtract the offset in the
    guest exit path.  In fact we just skip the whole path that switches
    back to host context, since we haven't switched to the guest context.
    Signed-off-by: NPaul Mackerras <paulus@samba.org>
    Signed-off-by: NAlexander Graf <agraf@suse.de>
    b4deba5c
kvm_host.h 17.2 KB