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authorGlauber Costa <glommer@redhat.com>2010-05-11 12:17:45 -0400
committerAvi Kivity <avi@redhat.com>2010-05-19 11:41:05 +0300
commit3a0d7256a6fb8c13f9fac6cd63250f97a8f0d8de (patch)
tree27a710b0f7e54c243382d47c290061699d0e755c /arch/x86
parent838815a78785022f6611e5c48386567aea7b818b (diff)
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>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/include/asm/kvm_para.h5
-rw-r--r--arch/x86/include/asm/pvclock-abi.h1
-rw-r--r--arch/x86/kernel/kvmclock.c3
-rw-r--r--arch/x86/kernel/pvclock.c4
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.