On Tue, 17 Oct 2023 at 18:19, Matias Ezequiel Vara Larsen <mvaralar@xxxxxxxxxx> wrote: > > Hello, > > This email is to clarify the VirtIO specification regarding the RELEASE > control request. Section 5.14.6.6.5.1 [1] states the following device > requirements for the RELEASE control request: > 1. The device MUST complete all pending I/O messages for the specified > stream ID. > 2. The device MUST NOT complete the control request while there are > pending I/O messages for the specified stream ID. > > The 1) requirement does not indicate what "complete" means. Does it mean > that the pending I/O messages in the tx queue shall be outputted in the > host, i.e., consumed by the audio backend? Or, completion means simply > to put the requests in the used-ring without consuming them? It means the latter. At no point is the host's consumption of audio data mentioned except for implicit or explicit period notifications. > > Regarding 2), I interpret it as "the device shall wait until all I/O > messages are proceeded to complete the RELEASE control request". Possible state transitions to RELEASE state are from PREPARE and STOP, which neither are associated with active I/O in the streams. The correct interpretation is "Do not reply to the control request if you have pending I/O messages for this stream ID". > Currently, the kernel driver seems not expecting such a delay when the > RELEASE command is sent. If I understand correctly, the kernel driver > first sends the RELEASE command and waits a fixed amount of time until > the device can process it. Then, the driver waits a fixed amount of time > until all pending IO messages are completed. If the device follows the > specification and waits until all messages IO are completed to issue the > completion of the RELEASE command, the kernel driver may timeout. The > time to complete N IO messages in the TX queue could be proportional > with the number of pending messages. > > In our device implementation [2], RELEASE is handled as follows: > - Drop all messages in the TX queue without outputting in the host. > - Complete the RELEASE control request. > > This seems to be working, however, I can observe that sometimes there > are still requests in the TX queue when we get RELEASE. Those requests > are never reproduced in the host. My guess is this is because of the guest alsa doing prebuffering, not that the host is supposed to handle those I/O messages. -- Manos _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
