• Marcelo Tosatti's avatar
    cpuidle: add haltpoll governor · 2cffe9f6
    Marcelo Tosatti authored
    The cpuidle_haltpoll governor, in conjunction with the haltpoll cpuidle
    driver, allows guest vcpus to poll for a specified amount of time before
    halting.
    This provides the following benefits to host side polling:
    
            1) The POLL flag is set while polling is performed, which allows
               a remote vCPU to avoid sending an IPI (and the associated
               cost of handling the IPI) when performing a wakeup.
    
            2) The VM-exit cost can be avoided.
    
    The downside of guest side polling is that polling is performed
    even with other runnable tasks in the host.
    
    Results comparing halt_poll_ns and server/client application
    where a small packet is ping-ponged:
    
    host                                        --> 31.33
    halt_poll_ns=300000 / no guest busy spin    --> 33.40   (93.8%)
    halt_poll_ns=0 / guest_halt_poll_ns=300000  --> 32.73   (95.7%)
    
    For the SAP HANA benchmarks (where idle_spin is a parameter
    of the previous version of the patch, results should be the
    same):
    
    hpns == halt_poll_ns
    
                              idle_spin=0/   idle_spin=800/    idle_spin=0/
                              hpns=200000    hpns=0            hpns=800000
    DeleteC06T03 (100 thread) 1.76           1.71 (-3%)        1.78   (+1%)
    InsertC16T02 (100 thread) 2.14           2.07 (-3%)        2.18   (+1.8%)
    DeleteC00T01 (1 thread)   1.34           1.28 (-4.5%)      1.29   (-3.7%)
    UpdateC00T03 (1 thread)   4.72           4.18 (-12%)       4.53   (-5%)
    Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    2cffe9f6
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