x86: KVM guest: use paravirt function to calculate cpu khz
We're currently facing timing problems in guests that do calibration under heavy load, and then the load vanishes. This means we'll have a much lower lpj than we actually should, and delays end up taking less time than they should, which is a nasty bug. Solution is to pass on the lpj value from host to guest, and have it preset. Signed-off-by: Glauber Costa <gcosta@redhat.com> Signed-off-by: Avi Kivity <avi@qumranet.com>
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@ -78,6 +78,34 @@ static cycle_t kvm_clock_read(void)
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return ret;
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}
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/*
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* If we don't do that, there is the possibility that the guest
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* will calibrate under heavy load - thus, getting a lower lpj -
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* and execute the delays themselves without load. This is wrong,
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* because no delay loop can finish beforehand.
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* Any heuristics is subject to fail, because ultimately, a large
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* poll of guests can be running and trouble each other. So we preset
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* lpj here
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*/
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static unsigned long kvm_get_tsc_khz(void)
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{
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return preset_lpj;
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}
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static void kvm_get_preset_lpj(void)
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{
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struct pvclock_vcpu_time_info *src;
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unsigned long khz;
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u64 lpj;
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src = &per_cpu(hv_clock, 0);
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khz = pvclock_tsc_khz(src);
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lpj = ((u64)khz * 1000);
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do_div(lpj, HZ);
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preset_lpj = lpj;
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}
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static struct clocksource kvm_clock = {
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.name = "kvm-clock",
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.read = kvm_clock_read,
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@ -153,6 +181,7 @@ void __init kvmclock_init(void)
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pv_time_ops.get_wallclock = kvm_get_wallclock;
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pv_time_ops.set_wallclock = kvm_set_wallclock;
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pv_time_ops.sched_clock = kvm_clock_read;
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pv_time_ops.get_tsc_khz = kvm_get_tsc_khz;
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#ifdef CONFIG_X86_LOCAL_APIC
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pv_apic_ops.setup_secondary_clock = kvm_setup_secondary_clock;
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#endif
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@ -163,6 +192,7 @@ void __init kvmclock_init(void)
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#ifdef CONFIG_KEXEC
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machine_ops.crash_shutdown = kvm_crash_shutdown;
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#endif
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kvm_get_preset_lpj();
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clocksource_register(&kvm_clock);
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}
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}
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