diff options
| author | rusty <rusty@0c8fb4dd-22a2-4bb5-bc14-6c75a5f43652> | 2013-09-25 04:44:11 +0000 |
|---|---|---|
| committer | rusty <rusty@0c8fb4dd-22a2-4bb5-bc14-6c75a5f43652> | 2013-09-25 04:44:11 +0000 |
| commit | f44fda41f15ee78db7d24a048177609228eca51a (patch) | |
| tree | 4e0d612cb55e9d428e755f5311479f5a3630e72d | |
| parent | 3e6f11baefbf36cbe10c5ae0a2b47c2794238406 (diff) | |
virtio-ccw: document GPR4/GPR2 cookie values
virtio-ccw on kvm can use a cookie value passed to guest
to optimize channel/VQ lookups.
Document this.
VIRTIO-29, approved OASIS meeting 2013-09-24.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
git-svn-id: https://tools.oasis-open.org/version-control/svn/virtio@44 0c8fb4dd-22a2-4bb5-bc14-6c75a5f43652
| -rw-r--r-- | virtio-v1.0-wd01-part1-specification.txt | 24 |
1 files changed, 23 insertions, 1 deletions
diff --git a/virtio-v1.0-wd01-part1-specification.txt b/virtio-v1.0-wd01-part1-specification.txt index a4e4223..dd0faea 100644 --- a/virtio-v1.0-wd01-part1-specification.txt +++ b/virtio-v1.0-wd01-part1-specification.txt @@ -1292,7 +1292,29 @@ For notifying the host of virtqueue buffers, the guest unfortunately can't use a channel command (the asynchronous characteristics of channel I/O interact badly with the host block I/O backend). Instead, it uses a diagnose 0x500 call with subcode -3 specifying the queue. +3 specifying the queue, as follows: + ++------+-------------------+--------------+ +| GPR | Input Value | Output Value | ++------+-------------------+--------------+ ++------+-------------------+--------------+ +| 1 | 0x3 | | ++------+-------------------+--------------+ +| 2 | Subchannel ID | Host Cookie | ++------+-------------------+--------------+ +| 3 | Virtqueue number | | ++------+-------------------+--------------+ +| 4 | Host Cookie | | ++------+-------------------+--------------+ + +Host cookie is an optional per-virtqueue 64 bit value that can be +used by the hypervisor to speed up the notification execution. +For each notification, the output value is returned in GPR2 and +should be passed in GPR4 for the next notification: + + info->cookie = do_notify(schid, + virtqueue_get_queue_index(vq), + info->cookie); 2.3.3.3.3. Early printk for Virtio Consoles ------------------------------------------- |