On 06/15/2010 01:30 AM, Marcelo Tosatti wrote:
Use information provided in exit_qualification to shortcut EOI path.
Reduces EOI latency from 4k to 2k cycles on Nehalem.
This already came up once - IIRC from Eddie Dong.
static int handle_apic_access(struct kvm_vcpu *vcpu)
{
+ unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
+ int access_type, offset;
+
+ access_type = (exit_qualification>> 12)& 0xf;
+ offset = exit_qualification& 0xfff;
+ if (access_type == 1&& offset == APIC_EOI) {
+ kvm_lapic_set_eoi(vcpu);
+ skip_emulated_instruction(vcpu);
+ return 1;
+ }
+
return emulate_instruction(vcpu, 0, 0, 0) == EMULATE_DONE;
}
This fails if the instruction is STOS, MOVS, or a RMW instruction as it
doesn't update registers and flags.
We could try to do tricks to detect this, but we already have x2apic for
Linux and the corresponding Hyper-V extension, which improve a lot of
other stuff, at least for newer guests.
\
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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