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Date: Fri, 07 Nov 2008 10:18:33 +0100
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: [Qemu-devel] vga slow with -enable-kvm
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To: qemu-devel@nongnu.org

  Hi,

The vga display is very slow when using latest svn with kvm enabled.
Just try to boot any linux kernel with vesafb enabled (vga=0x314 for
800x600@16), enjoy watching the boot messages scroll.  Booting without
kvm enabled is *faster*.

Feels like every single screen access is trapped or something like that.
kvm_stat confirms that, there are tons of mmio exits:

[root@zweiblum ~]# kvm_stat -1
efer_reload                    0         0
exits                   98234706    132054
fpu_reload               6330433         0
halt_exits                104372         0
halt_wakeup                    0         0
host_state_reload       96499874    132038
hypercalls                     0         0
insn_emulation          94632076    129954
insn_emulation_fail            0         0
invlpg                         0         0
io_exits                 2627489      1653
irq_exits                 239675       397
irq_window                 11138        14
largepages                     0         0
mmio_exits              93583132    129946
mmu_cache_miss             38079         0
mmu_flooded                37708         0
mmu_pde_zapped             35810         0
mmu_pte_updated           588299         0
mmu_pte_write             647324         0
mmu_recycled                   0         0
mmu_shadow_zapped          48191         0
pf_fixed                 1211070         1
pf_guest                  109462         0
remote_tlb_flush               0         0
request_irq                    0         0
signal_exits              164181       402
tlb_flush                 728218        44

cheers,
  Gerd