• MMIO exits are more expensive in KVM or Xen than in QEMU because they 
    involve, at least, privilege transitions.  However, MMIO write 
    operations can be effectively batched if those writes do not have side 
    effects.
    
    Good examples of this include VGA pixel operations when in a planar 
    mode.  As it turns out, we can get a nice boost in other areas too.  
    Laurent mentioned a 9.7% performance boost in iperf with the coalesced 
    MMIO changes for the e1000 when he originally posted this work for KVM.
    
    Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
    
    
    
    git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5961 c046a42c-6fe2-441c-8c8c-71466251a162
    aliguori authored
     
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