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Re: [Qemu-devel] [PATCH] virtio-net: do not start queues that are not en
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH] virtio-net: do not start queues that are not enabled by the guest |
Date: |
Thu, 21 Feb 2019 23:22:03 -0500 |
On Thu, Feb 21, 2019 at 10:10:08PM -0500, Michael S. Tsirkin wrote:
> On Fri, Feb 22, 2019 at 11:04:05AM +0800, Jason Wang wrote:
> >
> > On 2019/2/22 上午9:35, Michael S. Tsirkin wrote:
> > > On Thu, Feb 21, 2019 at 05:40:22PM +0800, Jason Wang wrote:
> > > > On 2019/2/21 下午4:18, Yuri Benditovich wrote:
> > > >
> > > > For 1.0 device, we can fix the queue_enable, but for 0.9x
> > > > device how do
> > > > you enable one specific queue in this case? (setting status?)
> > > >
> > > >
> > > > Do I understand correctly that for 0.9 device in some cases the
> > > > device will
> > > > receive feature _MQ set, but will not receive
> > > > VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET?
> > > > Or the problem is different?
> > > >
> > > >
> > > > Let me clarify, VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET is used to control the
> > > > the
> > > > number of queue pairs used by device for doing transmission and
> > > > reception. It
> > > > was not used to enable or disable a virtqueue.
> > > >
> > > > For 1.0 device, we should use queue_enable in pci cfg to enable and
> > > > disable
> > > > queue:
> > > >
> > > >
> > > > We could do:
> > > >
> > > > 1) allocate memory and set queue_enable for vq0
> > > >
> > > > 2) allocate memory and set queue_enable for vq1
> > > >
> > > > 3) Set vq paris to 1
> > > >
> > > > 4) allocate memory and set queue_enable for vq2
> > > >
> > > > 5) allocate memory and set queue_enable for vq3
> > > >
> > > > 6) set vq pairs to 2
> > >
> > > I do not think spec allows this.
> > >
> > >
> > > The driver MUST follow this sequence to initialize a device:
> > > 1. Reset the device.
> > > 2. Set the ACKNOWLEDGE status bit: the guest OS has noticed the device.
> > > 3. Set the DRIVER status bit: the guest OS knows how to drive the device.
> > > 4. Read device feature bits, and write the subset of feature bits
> > > understood by the OS and driver to the
> > > device. During this step the driver MAY read (but MUST NOT write) the
> > > device-specific configuration
> > > fields to check that it can support the device before accepting it.
> > > 5. Set the FEATURES_OK status bit. The driver MUST NOT accept new feature
> > > bits after this step.
> > > 6. Re-read device status to ensure the FEATURES_OK bit is still set:
> > > otherwise, the device does not
> > > support our subset of features and the device is unusable.
> > > 7. Perform device-specific setup, including discovery of virtqueues for
> > > the device, optional per-bus setup,
> > > reading and possibly writing the device’s virtio configuration space, and
> > > population of virtqueues.
> > > 8. Set the DRIVER_OK status bit. At this point the device is “live”.
> > >
> > >
> > > Thus vqs are setup at step 7.
> > >
> > > # of vq pairs are set up through a command which is a special
> > > buffer, and spec says:
> > >
> > > The driver MUST NOT send any buffer available notifications to the device
> > > before setting DRIVER_OK.
> >
> >
> > So you meant write to queue_enable is forbidden after DRIVER_OK (though it's
> > not very clear to me from the spec). And if a driver want to enable new
> > queues, it must reset the device?
>
>
> That's my reading. What do you think?
Btw some legacy drivers might violate this by addig buffers
before driver_ok.
>
> >
> > >
> > >
> > > > But this requires a proper implementation for queue_enable for vhost
> > > > which is
> > > > missed in qemu and probably what you really want to do.
> > > >
> > > > but for 0.9x device, there's no such way to do this. That's the issue.
> > > 0.9x there's no queue enable, assumption is PA!=0 means VQ has
> > > been enabled.
> > >
> > >
> > > > So
> > > > driver must allocate all queBes before starting the device, otherwise
> > > > there's
> > > > no way to enable it afterwards.
> > >
> > > As per spec queues must be allocated before DRIVER_OK.
> > >
> > > That is universal.
> >
> >
> > If I understand correctly, this is not what is done by current windows
> > drivers.
> >
> > Thanks
> >
> >
> > >
> > > > There're tricks to make it work like what is
> > > > done in your patch, but it depends on a specific implementation like
> > > > qemu which
> > > > is sub-optimal.
> > > >
> > > >
> > > >
> > > >
> > > > A fundamental question is what prevents you from just
> > > > initialization all
> > > > queues during driver start? It looks to me this save lots of
> > > > efforts
> > > > than allocating queue dynamically.
> > > >
> > > >
> > > > This is not so trivial in Windows driver, as it does not have
> > > > objects for queues
> > > > that it does not use. Linux driver first of all allocates all the
> > > > queues and then
> > > > adds Rx/Tx to those it will use. Windows driver first decides how
> > > > many queues
> > > > it will use then allocates objects for them and initializes them
> > > > from zero to
> > > > fully functional state.
> > > >
> > > >
> > > > Well, you just need to allocate some memory for the virtqueue, there's
> > > > no need
> > > > to make it visible to the rest until it was enabled.
> > > >
> > > > Thanks
> > > >
> > > >
> > > >
> > > >
- Re: [Qemu-devel] [PATCH] virtio-net: do not start queues that are not enabled by the guest, (continued)
- Re: [Qemu-devel] [PATCH] virtio-net: do not start queues that are not enabled by the guest, Yuri Benditovich, 2019/02/21
- Re: [Qemu-devel] [PATCH] virtio-net: do not start queues that are not enabled by the guest, Jason Wang, 2019/02/21
- Re: [Qemu-devel] [PATCH] virtio-net: do not start queues that are not enabled by the guest, Yuri Benditovich, 2019/02/21
- Re: [Qemu-devel] [PATCH] virtio-net: do not start queues that are not enabled by the guest, Jason Wang, 2019/02/21
- Re: [Qemu-devel] [PATCH] virtio-net: do not start queues that are not enabled by the guest, Michael S. Tsirkin, 2019/02/21
- Re: [Qemu-devel] [PATCH] virtio-net: do not start queues that are not enabled by the guest, Jason Wang, 2019/02/21
- Re: [Qemu-devel] [PATCH] virtio-net: do not start queues that are not enabled by the guest, Michael S. Tsirkin, 2019/02/21
- Re: [Qemu-devel] [PATCH] virtio-net: do not start queues that are not enabled by the guest,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [PATCH] virtio-net: do not start queues that are not enabled by the guest, Jason Wang, 2019/02/25
- Re: [Qemu-devel] [PATCH] virtio-net: do not start queues that are not enabled by the guest, Michael S. Tsirkin, 2019/02/25
- Re: [Qemu-devel] [PATCH] virtio-net: do not start queues that are not enabled by the guest, Michael S. Tsirkin, 2019/02/28