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Subject: Re: [virtio-comment] Re: [PATCH 0/2] Selective queue enabling
On Wed, Jun 7, 2023 at 10:59âAM Michael S. Tsirkin <mst@redhat.com> wrote: > > On Wed, Jun 07, 2023 at 10:47:12AM +0200, Eugenio Perez Martin wrote: > > On Wed, Jun 7, 2023 at 10:23âAM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote: > > > > > > On Wed, 7 Jun 2023 07:35:58 +0200, Eugenio Perez Martin <eperezma@redhat.com> wrote: > > > > On Tue, Jun 6, 2023 at 9:10âPM Michael S. Tsirkin <mst@redhat.com> wrote: > > > > > > > > > > On Tue, Jun 06, 2023 at 07:55:09PM +0200, Eugenio PÃrez wrote: > > > > > > This series allows the driver to start the device (as set DRIVER_OK) with only > > > > > > some queues enabled, and then enable another queues later. > > > > > > > > > > > > This is the current way to migrate net device state through control > > > > > > virtqueue, in a software assisted framework with vDPA: > > > > > > * First, only net CVQ is enabled at DRIVER_OK > > > > > > * All the control commands (mac address, mq, etc) needed for the device > > > > > > to behave the same as the source of migration are sent > > > > > > * Finally all the dataplane queues are enabled. > > > > > > > > > > In my opinion, this is somewhat problematic. Specifically, currently > > > > > devices tend to deduce how many queues are needed by looking > > > > > at the state at DRIVER_OK time. > > > > > > > > > > Question: what is wrong with enabling queues initially and then > > > > > doing a reset right after DRIVER_OK? You can even allocate > > > > > memory for just one queue (zeroing it out). > > > > > > > > > > Granted this looks kind of ugly but side-steps this problem with > > > > > no need for spec changes. > > > > > > > > > > > > > The problem is that the rx queues can start receiving, as the guest > > > > already has buffers there. > > > > > > Can we reset the vq before filling buffers to it? > > > > > > > They are passthrough from the guest so there is a window where the > > device can process rx descriptors. > > Not if there are no descriptors there. > But the migration is driven by the hypervisor, and it cannot control that. The guest will likely have rx descriptors available. > > > > > Apart from that, the back and forth > > > > introduces latencies. > > > > > > > > Maybe a better angle is to start all the queues as if they're reset, > > > > write 1 just to CVQ, configure the device, and then write 1 to all > > > > dataplane vqs? > > > > > > write to what? > > > > > > > Sorry I was unclear, I mean to enable the vqs writing 1 to queue_enable. > > > > Thanks! > > > > > Thanks. > > > > > > > > > > > Thanks! > > > > > > > > > > Eugenio PÃrez (2): > > > > > > virtio: introduce selective queue enabling > > > > > > virtio: pci support virtqueue selective enabling > > > > > > > > > > > > content.tex | 15 +++++++++++++-- > > > > > > transport-pci.tex | 4 ++++ > > > > > > 2 files changed, 17 insertions(+), 2 deletions(-) > > > > > > > > > > > > -- > > > > > > 2.31.1 > > > > > > > > > > > > > > > > > > > > > This publicly archived list offers a means to provide input to the > > > OASIS Virtual I/O Device (VIRTIO) TC. > > > > > > In order to verify user consent to the Feedback License terms and > > > to minimize spam in the list archive, subscription is required > > > before posting. > > > > > > Subscribe: virtio-comment-subscribe@lists.oasis-open.org > > > Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org > > > List help: virtio-comment-help@lists.oasis-open.org > > > List archive: https://lists.oasis-open.org/archives/virtio-comment/ > > > Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf > > > List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists > > > Committee: https://www.oasis-open.org/committees/virtio/ > > > Join OASIS: https://www.oasis-open.org/join/ > > > >
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