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Groups > linux.kernel > #1713725

Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array

From Cornelia Huck <cohuck@redhat.com>
Newsgroups linux.kernel
Subject Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array
Date 2017-08-17 11:30 +0200
Message-ID <ufphM-2RP-23@gated-at.bofh.it> (permalink)
References <ufcud-2Ob-1@gated-at.bofh.it> <ufn6i-1qg-5@gated-at.bofh.it> <ufnzk-1Dq-21@gated-at.bofh.it> <ufp86-2O3-19@gated-at.bofh.it>
Organization Red Hat GmbH

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On Thu, 17 Aug 2017 11:16:59 +0200
Paolo Bonzini <pbonzini@redhat.com> wrote:

> On 17/08/2017 09:36, Cornelia Huck wrote:
> >> What if we just sent a "vcpu move" request to all vcpus with the new 
> >> pointer after it moved? That way the vcpu thread itself would be 
> >> responsible for the migration to the new memory region. Only if all 
> >> vcpus successfully moved, keep rolling (and allow foreign get_vcpu again).
> >>
> >> That way we should be basically lock-less and scale well. For additional 
> >> icing, feel free to increase the vcpu array x2 every time it grows to 
> >> not run into the slow path too often.  
> > 
> > I'd prefer the rcu approach: This is a mechanism already understood
> > well, no need to come up with a new one that will likely have its own
> > share of problems.  
> 
> What Alex is proposing _is_ RCU, except with a homegrown
> synchronize_rcu.  Using kvm->srcu seems to be the best of both worlds.

I'm worried a bit about the 'homegrown' part, though.

I also may be misunderstanding what Alex means with "vcpu move"...

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[PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array Radim Krčmář <rkrcmar@redhat.com> - 2017-08-16 21:50 +0200
  [PATCH RFC 1/2] KVM: remove unused __KVM_HAVE_ARCH_VM_ALLOC Radim Krčmář <rkrcmar@redhat.com> - 2017-08-16 21:50 +0200
    Re: [PATCH RFC 1/2] KVM: remove unused __KVM_HAVE_ARCH_VM_ALLOC Christian Borntraeger <borntraeger@de.ibm.com> - 2017-08-21 15:50 +0200
  [PATCH RFC 2/2] KVM: RCU protected dynamic vcpus array Radim Krčmář <rkrcmar@redhat.com> - 2017-08-16 21:50 +0200
    Re: [PATCH RFC 2/2] KVM: RCU protected dynamic vcpus array Cornelia Huck <cohuck@redhat.com> - 2017-08-17 10:10 +0200
    Re: [PATCH RFC 2/2] KVM: RCU protected dynamic vcpus array David Hildenbrand <david@redhat.com> - 2017-08-17 13:20 +0200
      Re: [PATCH RFC 2/2] KVM: RCU protected dynamic vcpus array Paolo Bonzini <pbonzini@redhat.com> - 2017-08-17 19:00 +0200
      Re: [PATCH RFC 2/2] KVM: RCU protected dynamic vcpus array Radim Krčmář <rkrcmar@redhat.com> - 2017-08-17 19:00 +0200
  Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array Alexander Graf <agraf@suse.de> - 2017-08-17 09:10 +0200
    Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array Cornelia Huck <cohuck@redhat.com> - 2017-08-17 09:40 +0200
      Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array Paolo Bonzini <pbonzini@redhat.com> - 2017-08-17 11:20 +0200
        Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array Cornelia Huck <cohuck@redhat.com> - 2017-08-17 11:30 +0200
          Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array Paolo Bonzini <pbonzini@redhat.com> - 2017-08-17 11:50 +0200
            Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array David Hildenbrand <david@redhat.com> - 2017-08-17 12:00 +0200
              Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array Paolo Bonzini <pbonzini@redhat.com> - 2017-08-17 12:20 +0200
                Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array David Hildenbrand <david@redhat.com> - 2017-08-17 12:30 +0200
                Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array Paolo Bonzini <pbonzini@redhat.com> - 2017-08-17 12:30 +0200
                Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array David Hildenbrand <david@redhat.com> - 2017-08-17 12:40 +0200
    Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array Radim Krčmář <rkrcmar@redhat.com> - 2017-08-17 17:00 +0200
      Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array Alexander Graf <agraf@suse.de> - 2017-08-17 21:20 +0200
        Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array Radim Krčmář <rkrcmar@redhat.com> - 2017-08-18 16:20 +0200
          Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array Marc Zyngier <marc.zyngier@arm.com> - 2017-08-18 16:30 +0200
  Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array Cornelia Huck <cohuck@redhat.com> - 2017-08-17 09:40 +0200
  Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array David Hildenbrand <david@redhat.com> - 2017-08-17 09:40 +0200

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