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USB: fix latency in uhci-hcd and ohci-hcd

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Commits c44b225077bb1fb25ed5cd5c4f226897b91bedd4 (UHCI: implement new
semantics for URB_ISO_ASAP) and
6a41b4d3fe8cd4cc95181516fc6fba7b1747a27c (OHCI: implement new
semantics for URB_ISO_ASAP) increased the latency for isochronous URBs
in uhci-hcd and ohci-hcd respectively to 2 milliseconds, in an
attempt to avoid underruns.  It turns out that not only was this
unnecessary -- 1-ms latency works okay -- it also causes problems with
certain application loads such as real-time audio.

This patch changes the latency for both drivers back to 1 ms.

This should be applied to -stable kernels going back to 3.8.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-and-tested-by: Joe Rayhawk <jrayhawk@fairlystable.org>
CC: Clemens Ladisch <clemens@ladisch.de>
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alan Stern 2013-05-14 13:57:19 -04:00 committed by Greg Kroah-Hartman
parent 997ff89360
commit e194401783
2 changed files with 2 additions and 2 deletions
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2
drivers/usb/host/ohci-hcd.c
View File

@ -233,7 +233,7 @@ static int ohci_urb_enqueue (
urb->start_frame = frame; urb->start_frame = frame;
} }
} else if (ed->type == PIPE_ISOCHRONOUS) { } else if (ed->type == PIPE_ISOCHRONOUS) {
u16 next = ohci_frame_no(ohci) + 2; u16 next = ohci_frame_no(ohci) + 1;
u16 frame = ed->last_iso + ed->interval; u16 frame = ed->last_iso + ed->interval;
/* Behind the scheduling threshold? */ /* Behind the scheduling threshold? */

2
drivers/usb/host/uhci-q.c
View File

@ -1287,7 +1287,7 @@ static int uhci_submit_isochronous(struct uhci_hcd *uhci, struct urb *urb,
return -EINVAL; /* Can't change the period */ return -EINVAL; /* Can't change the period */
} else { } else {
next = uhci->frame_number + 2; next = uhci->frame_number + 1;
/* Find the next unused frame */ /* Find the next unused frame */
if (list_empty(&qh->queue)) { if (list_empty(&qh->queue)) {