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| author | Paolo Bonzini <pbonzini@redhat.com> | 2014-03-27 09:51:52 +0100 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2014-07-11 09:13:56 +0200 |
| commit | 98eb2f8b145cee711984d42eff5d6f19b6b1df69 (patch) | |
| tree | da28ce5a2a8dd362479ca4bd4d165254823c439f /arch/x86/kvm/vmx.c | |
| parent | 22d48b2d2aa0b078816eaa1e15e485811a2d03fa (diff) | |
| download | lwn-98eb2f8b145cee711984d42eff5d6f19b6b1df69.tar.gz lwn-98eb2f8b145cee711984d42eff5d6f19b6b1df69.zip | |
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>
Diffstat (limited to 'arch/x86/kvm/vmx.c')
| -rw-r--r-- | arch/x86/kvm/vmx.c | 5 |
1 files changed, 2 insertions, 3 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 8748c2e19ed6..5c7bbde25bbf 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -3672,7 +3672,7 @@ static void vmx_set_segment(struct kvm_vcpu *vcpu, vmcs_write32(sf->ar_bytes, vmx_segment_access_rights(var)); out: - vmx->emulation_required |= emulation_required(vcpu); + vmx->emulation_required = emulation_required(vcpu); } static void vmx_get_cs_db_l_bits(struct kvm_vcpu *vcpu, int *db, int *l) @@ -5640,7 +5640,7 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu) cpu_exec_ctrl = vmcs_read32(CPU_BASED_VM_EXEC_CONTROL); intr_window_requested = cpu_exec_ctrl & CPU_BASED_VIRTUAL_INTR_PENDING; - while (!guest_state_valid(vcpu) && count-- != 0) { + while (vmx->emulation_required && count-- != 0) { if (intr_window_requested && vmx_interrupt_allowed(vcpu)) return handle_interrupt_window(&vmx->vcpu); @@ -5674,7 +5674,6 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu) schedule(); } - vmx->emulation_required = emulation_required(vcpu); out: return ret; } |