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authorKevin Tian <kevin.tian@intel.com>2011-08-30 13:56:17 +0300
committerAvi Kivity <avi@redhat.com>2011-09-25 19:52:17 +0300
commit58fbbf26eb01cf6d92cf18da8d14b3a4af9c4b47 (patch)
tree738874a15a233eed6e2e18d9cfe99f09482e8b17 /arch/x86/kvm/vmx.c
parent45133ecaaec7aea447afc98cc2c24aac638bbe5c (diff)
downloadblackbird-op-linux-58fbbf26eb01cf6d92cf18da8d14b3a4af9c4b47.tar.gz
blackbird-op-linux-58fbbf26eb01cf6d92cf18da8d14b3a4af9c4b47.zip
KVM: APIC: avoid instruction emulation for EOI writes
Instruction emulation for EOI writes can be skipped, since sane guest simply uses MOV instead of string operations. This is a nice improvement when guest doesn't support x2apic or hyper-V EOI support. a single VM bandwidth is observed with ~8% bandwidth improvement (7.4Gbps->8Gbps), by saving ~5% cycles from EOI emulation. Signed-off-by: Kevin Tian <kevin.tian@intel.com> <Based on earlier work from>: Signed-off-by: Eddie Dong <eddie.dong@intel.com> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Avi Kivity <avi@redhat.com>
Diffstat (limited to 'arch/x86/kvm/vmx.c')
-rw-r--r--arch/x86/kvm/vmx.c21
1 files changed, 21 insertions, 0 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 5e8d411b0a81..47419d6031ea 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -71,6 +71,9 @@ module_param(vmm_exclusive, bool, S_IRUGO);
static int __read_mostly yield_on_hlt = 1;
module_param(yield_on_hlt, bool, S_IRUGO);
+static int __read_mostly fasteoi = 1;
+module_param(fasteoi, bool, S_IRUGO);
+
/*
* If nested=1, nested virtualization is supported, i.e., guests may use
* VMX and be a hypervisor for its own guests. If nested=0, guests may not
@@ -4540,6 +4543,24 @@ static int handle_xsetbv(struct kvm_vcpu *vcpu)
static int handle_apic_access(struct kvm_vcpu *vcpu)
{
+ if (likely(fasteoi)) {
+ unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
+ int access_type, offset;
+
+ access_type = exit_qualification & APIC_ACCESS_TYPE;
+ offset = exit_qualification & APIC_ACCESS_OFFSET;
+ /*
+ * Sane guest uses MOV to write EOI, with written value
+ * not cared. So make a short-circuit here by avoiding
+ * heavy instruction emulation.
+ */
+ if ((access_type == TYPE_LINEAR_APIC_INST_WRITE) &&
+ (offset == APIC_EOI)) {
+ kvm_lapic_set_eoi(vcpu);
+ skip_emulated_instruction(vcpu);
+ return 1;
+ }
+ }
return emulate_instruction(vcpu, 0) == EMULATE_DONE;
}
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