linux-kernel - [PATCH 6/6] KVM: perform a wake_up in kvm_make_all_cpus

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Date:   Thu,  6 Apr 2017 22:20:56 +0200
From:   Radim Krčmář <rkrcmar@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Christoffer Dall <cdall@...aro.org>,
        Andrew Jones <drjones@...hat.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Cornelia Huck <cornelia.huck@...ibm.com>,
        James Hogan <james.hogan@...tec.com>,
        Paul Mackerras <paulus@...abs.org>
Subject: [PATCH 6/6] KVM: perform a wake_up in kvm_make_all_cpus_request

We want to have kvm_make_all_cpus_request() to be an optmized version of

  kvm_for_each_vcpu(i, vcpu, kvm) {
    kvm_make_request(vcpu, request);
    kvm_vcpu_kick(vcpu);
  }

and kvm_vcpu_kick() wakes up the target vcpu.  We know which requests do
not need the wake up and use it to optimize the loop.

Thanks to that, this patch doesn't change the behavior of current users
(the all don't need the wake up) and only prepares for future where the
wake up is going to be needed.

I think that most requests do not need the wake up, so we would flip the
bit then.

Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
---
 virt/kvm/kvm_main.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a486c6ad27a6..1db503bab3dc 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -186,6 +186,9 @@ bool kvm_make_all_cpus_request(struct kvm *kvm, unsigned int req)
 		/* Set ->requests bit before we read ->mode. */
 		smp_mb__after_atomic();
 
+		if (!(req & KVM_REQUEST_NO_WAKEUP))
+			kvm_vcpu_wake_up(vcpu);
+
 		if (cpus != NULL && cpu != -1 && cpu != me &&
 				kvm_arch_vcpu_should_kick(vcpu))
 			cpumask_set_cpu(cpu, cpus);
-- 
2.12.0