diff options
| author | Glauber Costa <glommer@redhat.com> | 2010-05-11 12:17:45 -0400 |
|---|---|---|
| committer | Avi Kivity <avi@redhat.com> | 2010-05-19 11:41:05 +0300 |
| commit | 3a0d7256a6fb8c13f9fac6cd63250f97a8f0d8de (patch) | |
| tree | 27a710b0f7e54c243382d47c290061699d0e755c | |
| parent | 838815a78785022f6611e5c48386567aea7b818b (diff) | |
| download | linux-3a0d7256a6fb8c13f9fac6cd63250f97a8f0d8de.tar.bz2 | |
x86, paravirt: don't compute pvclock adjustments if we trust the tsc
If the HV told us we can fully trust the TSC, skip any
correction
Signed-off-by: Glauber Costa <glommer@redhat.com>
Acked-by: Zachary Amsden <zamsden@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
| -rw-r--r-- | arch/x86/include/asm/kvm_para.h | 5 | ||||
| -rw-r--r-- | arch/x86/include/asm/pvclock-abi.h | 1 | ||||
| -rw-r--r-- | arch/x86/kernel/kvmclock.c | 3 | ||||
| -rw-r--r-- | arch/x86/kernel/pvclock.c | 4 |
4 files changed, 13 insertions, 0 deletions
diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h index f019f8cb182e..05eba5e9a8e8 100644 --- a/arch/x86/include/asm/kvm_para.h +++ b/arch/x86/include/asm/kvm_para.h @@ -21,6 +21,11 @@ */ #define KVM_FEATURE_CLOCKSOURCE2 3 +/* The last 8 bits are used to indicate how to interpret the flags field + * in pvclock structure. If no bits are set, all flags are ignored. + */ +#define KVM_FEATURE_CLOCKSOURCE_STABLE_BIT 24 + #define MSR_KVM_WALL_CLOCK 0x11 #define MSR_KVM_SYSTEM_TIME 0x12 diff --git a/arch/x86/include/asm/pvclock-abi.h b/arch/x86/include/asm/pvclock-abi.h index ec5c41ac4bef..35f2d1948ada 100644 --- a/arch/x86/include/asm/pvclock-abi.h +++ b/arch/x86/include/asm/pvclock-abi.h @@ -39,5 +39,6 @@ struct pvclock_wall_clock { u32 nsec; } __attribute__((__packed__)); +#define PVCLOCK_TSC_STABLE_BIT (1 << 0) #endif /* __ASSEMBLY__ */ #endif /* _ASM_X86_PVCLOCK_ABI_H */ diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c index 59c740fcb9b3..eb9b76c716c2 100644 --- a/arch/x86/kernel/kvmclock.c +++ b/arch/x86/kernel/kvmclock.c @@ -215,4 +215,7 @@ void __init kvmclock_init(void) clocksource_register(&kvm_clock); pv_info.paravirt_enabled = 1; pv_info.name = "KVM"; + + if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT)) + pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT); } diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c index f5bc40e1697e..239427ca02af 100644 --- a/arch/x86/kernel/pvclock.c +++ b/arch/x86/kernel/pvclock.c @@ -135,6 +135,10 @@ cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src) barrier(); } while (version != src->version); + if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) && + (shadow.flags & PVCLOCK_TSC_STABLE_BIT)) + return ret; + /* * Assumption here is that last_value, a global accumulator, always goes * forward. If we are less than that, we should not be much smaller. |