USB: EHCI: stagger frames for interrupt transfers

This patch (as1243) tries to improve ehci-hcd's scheduling of
interrupt transfers.  Instead of trying to cram all transfers with the
same period into the same frame, the new code will spread the
transfers out among lots of different frames.  This should reduce the
periodic schedule load in any one frame -- some host controllers have
trouble when there's too much work to do.

A more thorough approach would stagger the uframe values as well.  But
this is enough to make a big improvement.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Dwayne Fontenot <dwayne.fontenot@att.net>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 6 insertions, 3 deletions

diff --git a/drivers/usb/host/ehci-sched.c b/drivers/usb/host/ehci-sched.c
index 556d0ec0c1f8..9d1babc7ff65 100644
--- a/drivers/usb/host/ehci-sched.c
+++ b/drivers/usb/host/ehci-sched.c
@@ -760,8 +760,10 @@ static int qh_schedule(struct ehci_hcd *ehci, struct ehci_qh *qh)
         if (status) {
                 /* "normal" case, uframing flexible except with splits */
                 if (qh->period) {
-                        frame = qh->period - 1;
-                        do {
+                        int             i;
+
+                        for (i = qh->period; status && i > 0; --i) {
+                                frame = ++ehci->random_frame % qh->period;
                                 for (uframe = 0; uframe < 8; uframe++) {
                                         status = check_intr_schedule (ehci,
                                                         frame, uframe, qh,
@@ -769,7 +771,7 @@ static int qh_schedule(struct ehci_hcd *ehci, struct ehci_qh *qh)
                                         if (status == 0)
                                                 break;
                                 }
-                        } while (status && frame--);
+                        }
 
                 /* qh->period == 0 means every uframe */
                 } else {
diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
index 6cff195e1a36..90ad3395bb21 100644
--- a/drivers/usb/host/ehci.h
+++ b/drivers/usb/host/ehci.h
@@ -116,6 +116,7 @@ struct ehci_hcd {			/* one per controller */
         struct timer_list       watchdog;
         unsigned long           actions;
         unsigned                stamp;
+        unsigned                random_frame;
         unsigned long           next_statechange;
         u32                     command;