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uhci: Retry to fill the queue while waiting for td completion

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If the guest is using multiple transfers to try and keep the usb bus busy /
used at maximum efficiency, currently we would see / do the following:

1) submit transfer 1 to the device
2) submit transfer 2 to the device
3) report transfer 1 completion to guest
4) report transfer 2 completion to guest
5) submit transfer 1 to the device
6) report transfer 1 completion to guest
7) submit transfer 2 to the device
8) report transfer 2 completion to guest
etc.

So after the initial submission we would effectively only have 1 transfer
in flight, rather then 2. This is caused by us not checking the queue for
addition of new transfers by the guest (ie the resubmission of a recently
finished transfer), while waiting for a pending transfer to complete.
This patch does add a check for this, changing the sequence to:

1) submit transfer 1 to the device
2) submit transfer 2 to the device
3) report transfer 1 completion to guest
4) submit transfer 1 to the device
5) report transfer 2 completion to guest
6) submit transfer 2 to the device
etc.

Thus keeping 2 transfers in flight (most of the time, and always 1),
as intended by the guest.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
This commit is contained in:
Hans de Goede 2012-10-24 18:31:19 +02:00 committed by Gerd Hoffmann
parent 3905097ea8
commit 8928c9c43d
1 changed files with 13 additions and 3 deletions
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16
hw/usb/hcd-uhci.c
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@ -110,7 +110,7 @@ struct UHCIQueue {
UHCIState *uhci;
USBEndpoint *ep;
QTAILQ_ENTRY(UHCIQueue) next;
QTAILQ_HEAD(, UHCIAsync) asyncs;
QTAILQ_HEAD(asyncs_head, UHCIAsync) asyncs;
int8_t valid;
};
@ -843,15 +843,25 @@ static int uhci_handle_td(UHCIState *s, UHCIQueue *q, uint32_t qh_addr,
}
if (async) {
if (!async->done)
return TD_RESULT_ASYNC_CONT;
if (queuing) {
/* we are busy filling the queue, we are not prepared
to consume completed packages then, just leave them
in async state */
return TD_RESULT_ASYNC_CONT;
}
if (!async->done) {
UHCI_TD last_td;
UHCIAsync *last = QTAILQ_LAST(&async->queue->asyncs, asyncs_head);
/*
* While we are waiting for the current td to complete, the guest
* may have added more tds to the queue. Note we re-read the td
* rather then caching it, as we want to see guest made changes!
*/
uhci_read_td(s, &last_td, last->td_addr);
uhci_queue_fill(async->queue, &last_td);
return TD_RESULT_ASYNC_CONT;
}
uhci_async_unlink(async);
goto done;
}