Commit e1944017 authored May 14, 2013 by Alan Stern Committed by Greg Kroah-Hartman May 15, 2013

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



Commits c44b2250 (UHCI: implement new
semantics for URB_ISO_ASAP) and
6a41b4d3 (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>

parent 997ff893

drivers/usb/host/ohci-hcd.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -233,7 +233,7 @@ static int ohci_urb_enqueue (
		urb->start_frame = frame;
		}
		} 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;

		/* Behind the scheduling threshold? */

drivers/usb/host/uhci-q.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1287,7 +1287,7 @@ static int uhci_submit_isochronous(struct uhci_hcd uhci, struct urb urb,
		return -EINVAL; /* Can't change the period */

		} else {
		next = uhci->frame_number + 2;
		next = uhci->frame_number + 1;

		/* Find the next unused frame */
		if (list_empty(&qh->queue)) {