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Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate
From: |
Avi Kivity |
Subject: |
Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd |
Date: |
Wed, 14 Mar 2012 12:05:56 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:10.0.1) Gecko/20120216 Thunderbird/10.0.1 |
On 03/14/2012 11:59 AM, Stefan Hajnoczi wrote:
> On Wed, Mar 14, 2012 at 9:22 AM, Avi Kivity <address@hidden> wrote:
> > On 03/13/2012 12:42 PM, Amos Kong wrote:
> >> Boot up guest with 232 virtio-blk disk, qemu will abort for fail to
> >> allocate ioeventfd. This patchset changes kvm_has_many_ioeventfds(),
> >> and check if available ioeventfd exists. If not, virtio-pci will
> >> fallback to userspace, and don't use ioeventfd for io notification.
> >
> > How about an alternative way of solving this, within the memory core:
> > trap those writes in qemu and write to the ioeventfd yourself. This way
> > ioeventfds work even without kvm:
> >
> >
> > core: create eventfd
> > core: install handler for memory address that writes to ioeventfd
> > kvm (optional): install kernel handler for ioeventfd
> >
> > even if the third step fails, the ioeventfd still works, it's just slower.
>
> That approach will penalize guests with large numbers of disks - they
> see an extra switch to vcpu thread instead of kvm.ko -> iothread.
It's only a failure path. The normal path is expected to have a kvm
ioeventfd installed.
> It
> seems okay provided we can solve the limit in the kernel once and for
> all by introducing a more dynamic data structure for in-kernel
> devices. That way future kernels will never hit an arbitrary limit
> below their file descriptor rlimit.
>
> Is there some reason why kvm.ko must use a fixed size array? Would it
> be possible to use a tree (maybe with a cache for recent lookups)?
It does use bsearch today IIRC. We'll expand the limit, but there must
be a limit, and qemu must be prepared to deal with it.
--
error compiling committee.c: too many arguments to function
- Re: [Qemu-devel] [PATCH 1/2] return available ioeventfds count in kvm_has_many_ioeventfds(), (continued)
- Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd, Stefan Hajnoczi, 2012/03/13
- Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd, Amos Kong, 2012/03/13
- Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd, Stefan Hajnoczi, 2012/03/13
- Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd, Amos Kong, 2012/03/13
- Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd, Stefan Hajnoczi, 2012/03/13
- Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd, Amos Kong, 2012/03/13
- Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd, Stefan Hajnoczi, 2012/03/14
Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd, Avi Kivity, 2012/03/14
- Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd, Stefan Hajnoczi, 2012/03/14
- Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd,
Avi Kivity <=
- Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd, Stefan Hajnoczi, 2012/03/14
- Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd, Avi Kivity, 2012/03/14
- Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd, Stefan Hajnoczi, 2012/03/14
- Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd, Amos Kong, 2012/03/16
- Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd, Stefan Hajnoczi, 2012/03/19
- Re: [Qemu-devel] [PATCH 0/2] virtio-pci: fix abort when fail to allocate ioeventfd, Avi Kivity, 2012/03/19