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Commit 0293615f authored by Glauber Costa's avatar Glauber Costa Committed by Avi Kivity
Browse files

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: default avatarGlauber Costa <gcosta@redhat.com>
Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent 3807f345

arch/x86/kernel/kvmclock.c

+30 −0
Original line number Diff line number Diff line
@@ -78,6 +78,34 @@ static cycle_t kvm_clock_read(void) 
	return ret;

}



/*

 * If we don't do that, there is the possibility that the guest

 * will calibrate under heavy load - thus, getting a lower lpj -

 * and execute the delays themselves without load. This is wrong,

 * because no delay loop can finish beforehand.

 * Any heuristics is subject to fail, because ultimately, a large

 * poll of guests can be running and trouble each other. So we preset

 * lpj here

 */

static unsigned long kvm_get_tsc_khz(void)

{

	return preset_lpj;

}



static void kvm_get_preset_lpj(void)

{

	struct pvclock_vcpu_time_info *src;

	unsigned long khz;

	u64 lpj;



	src = &per_cpu(hv_clock, 0);

	khz = pvclock_tsc_khz(src);



	lpj = ((u64)khz * 1000);

	do_div(lpj, HZ);

	preset_lpj = lpj;

}



static struct clocksource kvm_clock = {

	.name = "kvm-clock",

	.read = kvm_clock_read,
@@ -153,6 +181,7 @@ void __init kvmclock_init(void) 
		pv_time_ops.get_wallclock = kvm_get_wallclock;

		pv_time_ops.set_wallclock = kvm_set_wallclock;

		pv_time_ops.sched_clock = kvm_clock_read;

		pv_time_ops.get_tsc_khz = kvm_get_tsc_khz;

#ifdef CONFIG_X86_LOCAL_APIC

		pv_apic_ops.setup_secondary_clock = kvm_setup_secondary_clock;

#endif
@@ -163,6 +192,7 @@ void __init kvmclock_init(void) 
#ifdef CONFIG_KEXEC

		machine_ops.crash_shutdown  = kvm_crash_shutdown;

#endif

		kvm_get_preset_lpj();

		clocksource_register(&kvm_clock);

	}

}