Re: pinning, tsc and apic

[Chris Wright <chrisw@sous-sol.org>]

* Anthony Liguori (anthony@codemonkey.ws) wrote:
>  From a quick look, I suspect that the number of wildly off TSC 
> calibrations correspond to the VMs that are misbehaving.  I think this 
> may mean that we have to re-examine the tsc delta computation.
> 
> 10_serial.log:time.c: Detected 1995.038 MHz processor.
> 11_serial.log:time.c: Detected 2363.195 MHz processor.
> 12_serial.log:time.c: Detected 2492.675 MHz processor.
> 13_serial.log:time.c: Detected 1995.061 MHz processor.
> 14_serial.log:time.c: Detected 1994.917 MHz processor.
> 15_serial.log:time.c: Detected 4100.735 MHz processor.
> 16_serial.log:time.c: Detected 2075.800 MHz processor.
> 17_serial.log:time.c: Detected 2674.350 MHz processor.
> 18_serial.log:time.c: Detected 1995.002 MHz processor.
> 19_serial.log:time.c: Detected 1994.978 MHz processor.
> 1_serial.log:time.c: Detected 4384.310 MHz processor.

Is this with pinning?  We at least know we're losing small bits on
migration.  From my measurements it's ~3000 (outliers are 10-20k).

Also, what happens if you roll back to kvm-userspace 7f5c4d15ece5?

I'm using this:

diff -up arch/x86/kvm/svm.c~svm arch/x86/kvm/svm.c
--- arch/x86/kvm/svm.c~svm	2008-04-16 19:49:44.000000000 -0700
+++ arch/x86/kvm/svm.c	2008-05-14 23:44:18.000000000 -0700
@@ -621,6 +621,13 @@ static void svm_free_vcpu(struct kvm_vcp
 	kmem_cache_free(kvm_vcpu_cache, svm);
 }
 
+static void svm_tsc_update(void *arg)
+{
+	struct vcpu_svm *svm = arg;
+	rdtscll(svm->vcpu.arch.host_tsc);
+
+}
+
 static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -633,6 +640,9 @@ static void svm_vcpu_load(struct kvm_vcp
 		 * Make sure that the guest sees a monotonically
 		 * increasing TSC.
 		 */
+		if (vcpu->cpu != -1)
+			smp_call_function_single(vcpu->cpu, svm_tsc_update,
+						 svm, 0, 1);
 		rdtscll(tsc_this);
 		delta = vcpu->arch.host_tsc - tsc_this;
 		svm->vmcb->control.tsc_offset += delta;


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