Author: mav
Date: Mon Mar 16 11:57:03 2015
New Revision: 280134
URL: https://svnweb.freebsd.org/changeset/base/280134
Log:
Report ARAT (APIC-Timer-always-running) feature for virtual CPU.
This makes FreeBSD guest to not avoid using LAPIC timer, preferring HPET
due to worries about non-existing for virtual CPUs deep sleep states.
Benchmarks of usleep(1) on guest and host show such extra latencies:
- 51us for virtual HPET,
- 22us for virtual LAPIC timer,
- 22us for host HPET and
- 3us for host LAPIC timer.
MFC after: 2 weeks
Modified:
head/sys/amd64/vmm/x86.c
Modified: head/sys/amd64/vmm/x86.c
==============================================================================
--- head/sys/amd64/vmm/x86.c Mon Mar 16 09:15:59 2015 (r280133)
+++ head/sys/amd64/vmm/x86.c Mon Mar 16 11:57:03 2015 (r280134)
@@ -361,6 +361,12 @@ x86_emulate_cpuid(struct vm *vm, int vcp
break;
case CPUID_0000_0006:
+ regs[0] = CPUTPM1_ARAT;
+ regs[1] = 0;
+ regs[2] = 0;
+ regs[3] = 0;
+ break;
+
case CPUID_0000_000A:
/*
* Handle the access, but report 0 for
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