tree da28ce5a2a8dd362479ca4bd4d165254823c439f
parent 22d48b2d2aa0b078816eaa1e15e485811a2d03fa
author Paolo Bonzini <pbonzini@redhat.com> 1395910312 +0100
committer Paolo Bonzini <pbonzini@redhat.com> 1405062836 +0200

KVM: vmx: speed up emulation of invalid guest state

About 25% of the time spent in emulation of invalid guest state
is wasted in checking whether emulation is required for the next
instruction.  However, this almost never changes except when a
segment register (or TR or LDTR) changes, or when there is a mode
transition (i.e. CR0 changes).

In fact, vmx_set_segment and vmx_set_cr0 already modify
vmx->emulation_required (except that the former for some reason
uses |= instead of just an assignment).  So there is no need to
call guest_state_valid in the emulation loop.

Emulation performance test results indicate 1650-2600 cycles
for common instructions, versus 2300-3200 before this patch on
a Sandy Bridge Xeon.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>