Commit 0b9f6c46 authored Nov 02, 2016 by Pan Xinhui Committed by Ingo Molnar Nov 22, 2016

x86/kvm: Support the vCPU preemption check



Support the vcpu_is_preempted() functionality under KVM. This will
enhance lock performance on overcommitted hosts (more runnable vCPUs
than physical CPUs in the system) as doing busy waits for preempted
vCPUs will hurt system performance far worse than early yielding.

Use struct kvm_steal_time::preempted to indicate that if a vCPU
is running or not.

Signed-off-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: David.Laight@ACULAB.COM
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: benh@kernel.crashing.org
Cc: boqun.feng@gmail.com
Cc: borntraeger@de.ibm.com
Cc: bsingharora@gmail.com
Cc: dave@stgolabs.net
Cc: jgross@suse.com
Cc: kernellwp@gmail.com
Cc: konrad.wilk@oracle.com
Cc: linuxppc-dev@lists.ozlabs.org
Cc: mpe@ellerman.id.au
Cc: paulmck@linux.vnet.ibm.com
Cc: paulus@samba.org
Cc: rkrcmar@redhat.com
Cc: virtualization@lists.linux-foundation.org
Cc: will.deacon@arm.com
Cc: xen-devel-request@lists.xenproject.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1478077718-37424-9-git-send-email-xinhui.pan@linux.vnet.ibm.com


[ Typo fixes. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 4ec6e863

arch/x86/include/uapi/asm/kvm_para.h

+3 −1

Original line number	Diff line number	Diff line
		@@ -45,7 +45,9 @@ struct kvm_steal_time {
		__u64 steal;
		__u32 version;
		__u32 flags;
		__u32 pad[12];
		__u8 preempted;
		__u8 u8_pad[3];
		__u32 pad[11];
		};

		#define KVM_STEAL_ALIGNMENT_BITS 5

arch/x86/kvm/x86.c

+16 −0

Original line number	Diff line number	Diff line
		@@ -2071,6 +2071,8 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
		&vcpu->arch.st.steal, sizeof(struct kvm_steal_time))))
		return;

		vcpu->arch.st.steal.preempted = 0;

		if (vcpu->arch.st.steal.version & 1)
		vcpu->arch.st.steal.version += 1; /* first time write, random junk */

		@@ -2826,8 +2828,22 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
		kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
		}

		static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
		{
		if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
		return;

		vcpu->arch.st.steal.preempted = 1;

		kvm_write_guest_offset_cached(vcpu->kvm, &vcpu->arch.st.stime,
		&vcpu->arch.st.steal.preempted,
		offsetof(struct kvm_steal_time, preempted),
		sizeof(vcpu->arch.st.steal.preempted));
		}

		void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
		{
		kvm_steal_time_set_preempted(vcpu);
		kvm_x86_ops->vcpu_put(vcpu);
		kvm_put_guest_fpu(vcpu);
		vcpu->arch.last_host_tsc = rdtsc();

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