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Re: [Qemu-devel] [PATCH 1/2] sched: add virt sched domain for the guest
From: |
Peter Zijlstra |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] sched: add virt sched domain for the guest |
Date: |
Wed, 23 May 2012 17:52:47 +0200 |
On Wed, 2012-05-23 at 08:23 -0700, Dave Hansen wrote:
> On 05/23/2012 01:48 AM, Peter Zijlstra wrote:
> > On Wed, 2012-05-23 at 16:34 +0800, Liu ping fan wrote:
> >> > so we need to migrate some of vcpus from node-B to node-A, or to
> >> > node-C.
> > This is absolutely broken, you cannot do that.
> >
> > A guest task might want to be node affine, it looks at the topology sets
> > a cpu affinity mask and expects to stay on that node.
> >
> > But then you come along, and flip one of those cpus to another node. The
> > guest task will now run on another node and get remote memory accesses.
>
> Insane, sure. But, if the node has physically gone away, what do we do?
> I think we've got to either kill the guest, or let it run somewhere
> suboptimal. Sounds like you're advocating killing it. ;)
You all seem terribly confused. If you want a guest that 100% mirrors
the host topology you need hard-binding of all vcpu threads and clearly
you're in trouble if you unplug a host cpu while there's still a vcpu
expecting to run there.
That's an administrator error and you get to keep the pieces, I don't
care.
In case you want simple virt-numa where a number of vcpus constitute a
vnode and have their memory all on the same node the vcpus are ran on,
what does it matter if you unplug something in the host? Just migrate
everything -- including memory.
But what Liu was proposing is completely insane and broken. You cannot
simply remap cpu:node relations. Wanting to do that shows a profound
lack of understanding.
Our kernel assumes that a cpu remains on the same node. All userspace
that does anything with NUMA assumes the same. You cannot change this.
- [Qemu-devel] [RFC] kvm: export host NUMA info to guest's scheduler, Liu Ping Fan, 2012/05/23
- [Qemu-devel] [PATCH 1/2] sched: add virt sched domain for the guest, Liu Ping Fan, 2012/05/23
- Re: [Qemu-devel] [PATCH 1/2] sched: add virt sched domain for the guest, Peter Zijlstra, 2012/05/23
- Re: [Qemu-devel] [PATCH 1/2] sched: add virt sched domain for the guest, Liu ping fan, 2012/05/23
- Re: [Qemu-devel] [PATCH 1/2] sched: add virt sched domain for the guest, Peter Zijlstra, 2012/05/23
- Re: [Qemu-devel] [PATCH 1/2] sched: add virt sched domain for the guest, Liu ping fan, 2012/05/23
- Re: [Qemu-devel] [PATCH 1/2] sched: add virt sched domain for the guest, Peter Zijlstra, 2012/05/23
- Re: [Qemu-devel] [PATCH 1/2] sched: add virt sched domain for the guest, Liu ping fan, 2012/05/23
- Re: [Qemu-devel] [PATCH 1/2] sched: add virt sched domain for the guest, Peter Zijlstra, 2012/05/23
- Re: [Qemu-devel] [PATCH 1/2] sched: add virt sched domain for the guest, Dave Hansen, 2012/05/23
- Re: [Qemu-devel] [PATCH 1/2] sched: add virt sched domain for the guest,
Peter Zijlstra <=
[Qemu-devel] [PATCH 2/2] sched: add virt domain device's driver, Liu Ping Fan, 2012/05/23
[Qemu-devel] [PATCH] kvm: collect vcpus' numa info for guest's scheduler, Liu Ping Fan, 2012/05/23
[Qemu-devel] [PATCH] Qemu: add virt sched domain device, Liu Ping Fan, 2012/05/23