linux-kernel - [ 003/127] USB: fix latency in uhci-hcd and ohci-hcd

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Message-Id: <20130605213218.397940486@linuxfoundation.org>
Date:	Wed,  5 Jun 2013 14:32:50 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Alan Stern <stern@...land.harvard.edu>,
	Clemens Ladisch <clemens@...isch.de>
Subject: [ 003/127] USB: fix latency in uhci-hcd and ohci-hcd

3.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alan Stern <stern@...land.harvard.edu>

commit e1944017839d7dfbf7329fac4bdec8b4050edf5e upstream.

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@...land.harvard.edu>
Reported-and-tested-by: Joe Rayhawk <jrayhawk@...rlystable.org>
CC: Clemens Ladisch <clemens@...isch.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/usb/host/ohci-hcd.c |    2 +-
 drivers/usb/host/uhci-q.c   |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/usb/host/ohci-hcd.c
+++ b/drivers/usb/host/ohci-hcd.c
@@ -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? */
--- a/drivers/usb/host/uhci-q.c
+++ b/drivers/usb/host/uhci-q.c
@@ -1287,7 +1287,7 @@ static int uhci_submit_isochronous(struc
 		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)) {


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