[PATCH v2 6/7] don't compute pvclock adjustments if we trust the tsc
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From: Glauber Costa on 3 May 2010 12:00 If the HV told us we can fully trust the TSC, skip any correction Signed-off-by: Glauber Costa <glommer(a)redhat.com> --- arch/x86/include/asm/kvm_para.h | 5 +++++ arch/x86/include/asm/pvclock-abi.h | 1 + arch/x86/kernel/kvmclock.c | 3 +++ 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 f019f8c..6f1b878 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_TSC 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 ec5c41a..b123bd7 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_STABLE_TSC (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 59c740f..518de01 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_TSC)) + pvclock_set_flags(PVCLOCK_STABLE_TSC); } diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c index 3dff5fa..0d4fe0c 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_STABLE_TSC) && + (shadow.flags & PVCLOCK_STABLE_TSC)) + 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. -- 1.6.2.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |