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Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver
From: |
Neo Jia |
Subject: |
Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver |
Date: |
Mon, 15 Aug 2016 22:43:53 -0700 |
User-agent: |
Mutt/1.6.2 (2016-07-01) |
On Tue, Aug 16, 2016 at 04:52:30AM +0000, Tian, Kevin wrote:
> > From: Neo Jia [mailto:address@hidden
> > Sent: Tuesday, August 16, 2016 12:17 PM
> >
> > On Tue, Aug 16, 2016 at 03:50:44AM +0000, Tian, Kevin wrote:
> > > > From: Neo Jia [mailto:address@hidden
> > > > Sent: Tuesday, August 16, 2016 11:46 AM
> > > >
> > > > On Tue, Aug 16, 2016 at 12:30:25AM +0000, Tian, Kevin wrote:
> > > > > > From: Neo Jia [mailto:address@hidden
> > > > > > Sent: Tuesday, August 16, 2016 3:59 AM
> > > >
> > > > > > > >
> > > > > > > > For NVIDIA vGPU solution we need to know all devices assigned
> > > > > > > > to a VM in
> > > > > > > > one shot to commit resources of all vGPUs assigned to a VM
> > > > > > > > along with
> > > > > > > > some common resources.
> > > > > > >
> > > > > > > Kirti, can you elaborate the background about above one-shot
> > > > > > > commit
> > > > > > > requirement? It's hard to understand such a requirement.
> > > > > > >
> > > > > > > As I relied in another mail, I really hope start/stop become a
> > > > > > > per-mdev
> > > > > > > attribute instead of global one, e.g.:
> > > > > > >
> > > > > > > echo "0/1" >
> > /sys/class/mdev/12345678-1234-1234-1234-123456789abc/start
> > > > > > >
> > > > > > > In many scenario the user space client may only want to talk to
> > > > > > > mdev
> > > > > > > instance directly, w/o need to contact its parent device. Still
> > > > > > > take
> > > > > > > live migration for example, I don't think Qemu wants to know
> > > > > > > parent
> > > > > > > device of assigned mdev instances.
> > > > > >
> > > > > > Hi Kevin,
> > > > > >
> > > > > > Having a global /sys/class/mdev/mdev_start doesn't require anybody
> > > > > > to know
> > > > > > parent device. you can just do
> > > > > >
> > > > > > echo "mdev_UUID" > /sys/class/mdev/mdev_start
> > > > > >
> > > > > > or
> > > > > >
> > > > > > echo "mdev_UUID" > /sys/class/mdev/mdev_stop
> > > > > >
> > > > > > without knowing the parent device.
> > > > > >
> > > > >
> > > > > You can look at some existing sysfs example, e.g.:
> > > > >
> > > > > echo "0/1" > /sys/bus/cpu/devices/cpu1/online
> > > > >
> > > > > You may also argue why not using a global style:
> > > > >
> > > > > echo "cpu1" > /sys/bus/cpu/devices/cpu_online
> > > > > echo "cpu1" > /sys/bus/cpu/devices/cpu_offline
> > > > >
> > > > > There are many similar examples...
> > > >
> > > > Hi Kevin,
> > > >
> > > > My response above is to your question about using the global sysfs
> > > > entry as you
> > > > don't want to have the global path because
> > > >
> > > > "I don't think Qemu wants to know parent device of assigned mdev
> > > > instances.".
> > > >
> > > > So I just want to confirm with you that (in case you miss):
> > > >
> > > > /sys/class/mdev/mdev_start | mdev_stop
> > > >
> > > > doesn't require the knowledge of parent device.
> > > >
> > >
> > > Qemu is just one example, where your explanation of parent device
> > > makes sense but still it's not good for Qemu to populate /sys/class/mdev
> > > directly. Qemu is passed with the actual sysfs path of assigned mdev
> > > instance, so any mdev attributes touched by Qemu should be put under
> > > that node (e.g. start/stop for live migration usage as I explained
> > > earlier).
> >
> > Exactly, qemu is passed with the actual sysfs path.
> >
> > So, QEMU doesn't touch the file /sys/class/mdev/mdev_start | mdev_stop at
> > all.
> >
> > QEMU will take the sysfs path as input:
> >
> > -device
> > vfio-pci,sysfsdev=/sys/bus/mdev/devices/c0b26072-dd1b-4340-84fe-bf338c510818-0,i
> > d=vgpu0
>
> no need of passing "id=vgpu0" here. If necessary you can put id as an
> attribute
> under sysfs mdev node:
>
> /sys/bus/mdev/devices/c0b26072-dd1b-4340-84fe-bf338c510818-0/id
I think we have moved away from the device index based on Alex's comment, so the
device path will be:
/sys/bus/mdev/devices/c0b26072-dd1b-4340-84fe-bf338c510818
>
> >
> > As you are saying in live migration, QEMU needs to access "start" and
> > "stop". Could you
> > please share more details, such as how QEMU access the "start" and "stop"
> > sysfs,
> > when and what triggers that?
> >
>
> A conceptual flow as below:
>
> 1. Quiescent mdev activity on the parent device (e.g. stop scheduling, wait
> for
> in-flight DMA completed, etc.)
>
> echo "0" > /sys/bus/mdev/devices/c0b26072-dd1b-4340-84fe-bf338c510818-0/start
>
> 2. Save mdev state:
>
> cat /sys/bus/mdev/devices/c0b26072-dd1b-4340-84fe-bf338c510818-0/state > xxx
>
> 3. xxx will be part of the final VM image and copied to a new machine
>
> 4. Allocate/prepare mdev on the new machine for this VM
>
> 5. Restore mdev state:
>
> cat xxx > /sys/bus/mdev/devices/c0b26072-dd1b-4340-84fe-bf338c510818-0/state
> (might be a different path name)
>
> 6. start mdev on the new parent device:
>
> echo "1" > /sys/bus/mdev/devices/c0b26072-dd1b-4340-84fe-bf338c510818-0/start
Thanks for the sequence, so based on above live migration, the access of
"start/stop"
are from other user space program not QEMU process.
(Just to be clear, I am not saying that I won't consider your suggestion of
accommodating the "start/stop" file from global to mdev node, but I do want to
point
out that keeping them inside global shouldn't impact your live migration
sequence
above.)
Thanks,
Neo
>
> Thanks
> Kevin
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver, (continued)
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver, Alex Williamson, 2016/08/15
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver, Neo Jia, 2016/08/15
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver, Tian, Kevin, 2016/08/15
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver, Neo Jia, 2016/08/16
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver, Alex Williamson, 2016/08/16
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver, Tian, Kevin, 2016/08/15
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver, Neo Jia, 2016/08/15
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver, Tian, Kevin, 2016/08/15
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver, Neo Jia, 2016/08/16
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver, Tian, Kevin, 2016/08/16
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver,
Neo Jia <=
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver, Tian, Kevin, 2016/08/16
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver, Neo Jia, 2016/08/16
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver, Alex Williamson, 2016/08/16
- Re: [Qemu-devel] [PATCH v6 1/4] vfio: Mediated device Core driver, Alex Williamson, 2016/08/16
[Qemu-devel] [PATCH v6 3/4] vfio iommu: Add support for mediated devices, Kirti Wankhede, 2016/08/03
[Qemu-devel] [PATCH v6 4/4] docs: Add Documentation for Mediated devices, Kirti Wankhede, 2016/08/03