From 9c8fd1ba2201c072bd3cf6940e2ca4d0a7aed723 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@redhat.com>
Date: Fri, 6 Feb 2015 12:58:42 +0100
Subject: [PATCH] KVM: x86: optimize delivery of TSC deadline timer interrupt

The newly-added tracepoint shows the following results on
the tscdeadline_latency test:

        qemu-kvm-8387  [002]  6425.558974: kvm_vcpu_wakeup:      poll time 10407 ns
        qemu-kvm-8387  [002]  6425.558984: kvm_vcpu_wakeup:      poll time 0 ns
        qemu-kvm-8387  [002]  6425.561242: kvm_vcpu_wakeup:      poll time 10477 ns
        qemu-kvm-8387  [002]  6425.561251: kvm_vcpu_wakeup:      poll time 0 ns

and so on.  This is because we need to go through kvm_vcpu_block again
after the timer IRQ is injected.  Avoid it by polling once before
entering kvm_vcpu_block.

On my machine (Xeon E5 Sandy Bridge) this removes about 500 cycles (7%)
from the latency of the TSC deadline timer.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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