linux-kernel - Re: [PATCH v2 3/7] KVM-HV: KVM Steal time implementation

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Date:	Tue, 28 Jun 2011 15:02:16 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Glauber Costa <glommer@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Anthony Liguori <aliguori@...ibm.com>,
	Eric B Munson <emunson@...bm.net>
Subject: Re: [PATCH v2 3/7] KVM-HV: KVM Steal time implementation

On Tue, Jun 28, 2011 at 09:30:29AM -0300, Glauber Costa wrote:
> On 06/20/2011 05:56 PM, Marcelo Tosatti wrote:
> >On Sun, Jun 19, 2011 at 12:57:53PM +0300, Avi Kivity wrote:
> >>On 06/17/2011 01:20 AM, Glauber Costa wrote:
> >>>To implement steal time, we need the hypervisor to pass the guest information
> >>>about how much time was spent running other processes outside the VM.
> >>>This is per-vcpu, and using the kvmclock structure for that is an abuse
> >>>we decided not to make.
> >>>
> >>>In this patchset, I am introducing a new msr, KVM_MSR_STEAL_TIME, that
> >>>holds the memory area address containing information about steal time
> >>>
> >>>This patch contains the hypervisor part for it. I am keeping it separate from
> >>>the headers to facilitate backports to people who wants to backport the kernel
> >>>part but not the hypervisor, or the other way around.
> >>>
> >>>
> >>>
> >>>+#define KVM_STEAL_ALIGNMENT_BITS 5
> >>>+#define KVM_STEAL_VALID_BITS ((-1ULL<<   (KVM_STEAL_ALIGNMENT_BITS + 1)))
> >>>+#define KVM_STEAL_RESERVED_MASK (((1<<   KVM_STEAL_ALIGNMENT_BITS) - 1 )<<   1)
> >>
> >>Clumsy, but okay.
> >>
> >>>+static void record_steal_time(struct kvm_vcpu *vcpu)
> >>>+{
> >>>+	u64 delta;
> >>>+
> >>>+	if (vcpu->arch.st.stime&&   vcpu->arch.st.this_time_out) {
> >>
> >>0 is a valid value for stime.
> >>
> >>>+
> >>>+		if (unlikely(kvm_read_guest(vcpu->kvm, vcpu->arch.st.stime,
> >>>+			&vcpu->arch.st.steal, sizeof(struct kvm_steal_time)))) {
> >>>+
> >>>+			vcpu->arch.st.stime = 0;
> >>>+			return;
> >>>+		}
> >>>+
> >>>+		delta = (get_kernel_ns() - vcpu->arch.st.this_time_out);
> >>>+
> >>>+		vcpu->arch.st.steal.steal += delta;
> >>>+		vcpu->arch.st.steal.version += 2;
> >>>+
> >>>+		if (unlikely(kvm_write_guest(vcpu->kvm, vcpu->arch.st.stime,
> >>>+			&vcpu->arch.st.steal, sizeof(struct kvm_steal_time)))) {
> >>>+
> >>>+			vcpu->arch.st.stime = 0;
> >>>+			return;
> >>>+		}
> >>>+	}
> >>>+
> >>>+}
> >>>+
> >>>
> >>>@@ -2158,6 +2206,8 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> >>>  			kvm_migrate_timers(vcpu);
> >>>  		vcpu->cpu = cpu;
> >>>  	}
> >>>+
> >>>+	record_steal_time(vcpu);
> >>>  }
> >>
> >>This records time spent in userspace in the vcpu thread as steal
> >>time.  Is this what we want?  Or just time preempted away?
> >
> >It also accounts halt time (kvm_vcpu_block) as steal time. Glauber, you
> >could instead use the "runnable-state-but-waiting-in-runqueue" field of
> >SCHEDSTATS, i forgot the exact name.
> >
> I thought about it in the past. I let the idea aside because I
> didn't want to introduce a dependency on SCHEDSTATS. But thinking
> about it again now (and after some days of experimentations with
> it), I think we could have both.
> 
> use run_delay (the field you were thinking of) when schedstats are
> available, and fallback to an estimate method like the one we're
> doing when it is not.
> 
> Objections ?

I'm okay with that.

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