Messages in this thread | | | Date | Mon, 23 May 2022 16:54:32 -0700 | Subject | Re: [PATCH 1/4] vdpa: Add stop operation | From | Si-Wei Liu <> |
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On 5/23/2022 12:20 PM, Eugenio Perez Martin wrote: > On Sat, May 21, 2022 at 12:13 PM Si-Wei Liu <si-wei.liu@oracle.com> wrote: >> >> >> On 5/20/2022 10:23 AM, Eugenio Pérez wrote: >>> This operation is optional: It it's not implemented, backend feature bit >>> will not be exposed. >>> >>> Signed-off-by: Eugenio Pérez <eperezma@redhat.com> >>> --- >>> include/linux/vdpa.h | 6 ++++++ >>> 1 file changed, 6 insertions(+) >>> >>> diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h >>> index 15af802d41c4..ddfebc4e1e01 100644 >>> --- a/include/linux/vdpa.h >>> +++ b/include/linux/vdpa.h >>> @@ -215,6 +215,11 @@ struct vdpa_map_file { >>> * @reset: Reset device >>> * @vdev: vdpa device >>> * Returns integer: success (0) or error (< 0) >>> + * @stop: Stop or resume the device (optional, but it must >>> + * be implemented if require device stop) >>> + * @vdev: vdpa device >>> + * @stop: stop (true), not stop (false) >>> + * Returns integer: success (0) or error (< 0) >> Is this uAPI meant to address all use cases described in the full blown >> _F_STOP virtio spec proposal, such as: >> >> --------------%<-------------- >> >> ...... the device MUST finish any in flight >> operations after the driver writes STOP. Depending on the device, it >> can do it >> in many ways as long as the driver can recover its normal operation if it >> resumes the device without the need of resetting it: >> >> - Drain and wait for the completion of all pending requests until a >> convenient avail descriptor. Ignore any other posterior descriptor. >> - Return a device-specific failure for these descriptors, so the driver >> can choose to retry or to cancel them. >> - Mark them as done even if they are not, if the kind of device can >> assume to lose them. >> --------------%<-------------- >> > Right, this is totally underspecified in this series. > > I'll expand on it in the next version, but that text proposed to > virtio-comment was complicated and misleading. I find better to get > the previous version description. Would the next description work? > > ``` > After the return of ioctl, the device MUST finish any pending operations like > in flight requests. It must also preserve all the necessary state (the > virtqueue vring base plus the possible device specific states) Hmmm, "possible device specific states" is a bit vague. Does it require the device to save any device internal state that is not defined in the virtio spec - such as any failed in-flight requests to resubmit upon resume? Or you would lean on SVQ to intercept it in depth and save it with some other means? I think network device also has internal state such as flow steering state that needs bookkeeping as well.
A follow-up question is what is the use of the `stop` argument of false, does it require the device to support resume? I seem to recall this is something to abandon in favor of device reset plus setting queue base/addr after. Or it's just a optional feature that may be device specific (if one can do so in simple way).
-Siwei
> that is required > for restoring in the future. > > In the future, we will provide features similar to VHOST_USER_GET_INFLIGHT_FD > so the device can save pending operations. > ``` > > Thanks for pointing it out! > > > > > >> E.g. do I assume correctly all in flight requests are flushed after >> return from this uAPI call? Or some of pending requests may be subject >> to loss or failure? How does the caller/user specify these various >> options (if there are) for device stop? >> >> BTW, it would be nice to add the corresponding support to vdpa_sim_blk >> as well to demo the stop handling. To just show it on vdpa-sim-net IMHO >> is perhaps not so convincing. >> >> -Siwei >> >>> * @get_config_size: Get the size of the configuration space includes >>> * fields that are conditional on feature bits. >>> * @vdev: vdpa device >>> @@ -316,6 +321,7 @@ struct vdpa_config_ops { >>> u8 (*get_status)(struct vdpa_device *vdev); >>> void (*set_status)(struct vdpa_device *vdev, u8 status); >>> int (*reset)(struct vdpa_device *vdev); >>> + int (*stop)(struct vdpa_device *vdev, bool stop); >>> size_t (*get_config_size)(struct vdpa_device *vdev); >>> void (*get_config)(struct vdpa_device *vdev, unsigned int offset, >>> void *buf, unsigned int len);
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