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Commit 0b9f6c46 authored by Pan Xinhui's avatar Pan Xinhui Committed by Ingo Molnar
Browse files

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: default avatarPan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarPaolo 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: default avatarIngo 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();