Commit e1be9ac8 authored Mar 26, 2020 by Wanpeng Li Committed by Paolo Bonzini Mar 26, 2020

KVM: X86: Narrow down the IPI fastpath to single target IPI



The original single target IPI fastpath patch forgot to filter the
ICR destination shorthand field. Multicast IPI is not suitable for
this feature since wakeup the multiple sleeping vCPUs will extend
the interrupt disabled time, it especially worse in the over-subscribe
and VM has a little bit more vCPUs scenario. Let's narrow it down to
single target IPI.

Two VMs, each is 76 vCPUs, one running 'ebizzy -M', the other
running cyclictest on all vCPUs, w/ this patch, the avg score
of cyclictest can improve more than 5%. (pv tlb, pv ipi, pv
sched yield are disabled during testing to avoid the disturb).

Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1585189202-1708-3-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 94be4b85

arch/x86/kvm/x86.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -1554,7 +1554,10 @@ EXPORT_SYMBOL_GPL(kvm_emulate_wrmsr);
		*/
		static int handle_fastpath_set_x2apic_icr_irqoff(struct kvm_vcpu *vcpu, u64 data)
		{
		if (lapic_in_kernel(vcpu) && apic_x2apic_mode(vcpu->arch.apic) &&
		if (!lapic_in_kernel(vcpu) \|\| !apic_x2apic_mode(vcpu->arch.apic))
		return 1;

		if (((data & APIC_SHORT_MASK) == APIC_DEST_NOSHORT) &&
		((data & APIC_DEST_MASK) == APIC_DEST_PHYSICAL) &&
		((data & APIC_MODE_MASK) == APIC_DM_FIXED)) {

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