USB: EHCI: simplify remainder computations

This patch (as1406) adds a micro-optimization to ehci-hcd's scheduling
code.  Instead of computing remainders with respect to the schedule
length, use bitwise-and (which is quicker).  We know that the schedule
length will always be a power of two, but the compiler doesn't have
this information.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: David Brownell <david-b@pacbell.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 15 insertions, 14 deletions

diff --git a/drivers/usb/host/ehci-sched.c b/drivers/usb/host/ehci-sched.c
index efadced4ae67..27dd841b9aa2 100644
--- a/drivers/usb/host/ehci-sched.c
+++ b/drivers/usb/host/ehci-sched.c
@@ -1417,7 +1417,7 @@ iso_stream_schedule (
         if (!stream->highspeed)
                 period <<= 3;
 
-        now = ehci_readl(ehci, &ehci->regs->frame_index) % mod;
+        now = ehci_readl(ehci, &ehci->regs->frame_index) & (mod - 1);
 
         /* Typical case: reuse current schedule, stream is still active.
          * Hopefully there are no gaps from the host falling behind
@@ -1461,7 +1461,7 @@ iso_stream_schedule (
          * jump until after the queue is primed.
          */
         start = SCHEDULE_SLOP + (now & ~0x07);
-        start %= mod;
+        start &= mod - 1;
         stream->next_uframe = start;
 
         /* NOTE:  assumes URB_ISO_ASAP, to limit complexity/bugs */
@@ -1483,7 +1483,7 @@ iso_stream_schedule (
 
                 /* schedule it here if there's enough bandwidth */
                 if (enough_space) {
-                        stream->next_uframe = start % mod;
+                        stream->next_uframe = start & (mod - 1);
                         goto ready;
                 }
         }
@@ -1599,7 +1599,7 @@ itd_link_urb (
         struct ehci_iso_sched   *iso_sched = urb->hcpriv;
         struct ehci_itd         *itd;
 
-        next_uframe = stream->next_uframe % mod;
+        next_uframe = stream->next_uframe & (mod - 1);
 
         if (unlikely (list_empty(&stream->td_list))) {
                 ehci_to_hcd(ehci)->self.bandwidth_allocated
@@ -1637,13 +1637,13 @@ itd_link_urb (
 
                 next_uframe += stream->interval;
                 stream->depth += stream->interval;
-                next_uframe %= mod;
+                next_uframe &= mod - 1;
                 packet++;
 
                 /* link completed itds into the schedule */
                 if (((next_uframe >> 3) != frame)
                                 || packet == urb->number_of_packets) {
-                        itd_link (ehci, frame % ehci->periodic_size, itd);
+                        itd_link(ehci, frame & (ehci->periodic_size - 1), itd);
                         itd = NULL;
                 }
         }
@@ -2020,7 +2020,7 @@ sitd_link_urb (
                         "sched devp %s ep%d%s-iso [%d] %dms/%04x\n",
                         urb->dev->devpath, stream->bEndpointAddress & 0x0f,
                         (stream->bEndpointAddress & USB_DIR_IN) ? "in" : "out",
-                        (next_uframe >> 3) % ehci->periodic_size,
+                        (next_uframe >> 3) & (ehci->periodic_size - 1),
                         stream->interval, hc32_to_cpu(ehci, stream->splits));
                 stream->start = jiffies;
         }
@@ -2043,13 +2043,13 @@ sitd_link_urb (
                 sitd->urb = urb;
 
                 sitd_patch(ehci, stream, sitd, sched, packet);
-                sitd_link (ehci, (next_uframe >> 3) % ehci->periodic_size,
+                sitd_link(ehci, (next_uframe >> 3) & (ehci->periodic_size - 1),
                                 sitd);
 
                 next_uframe += stream->interval << 3;
                 stream->depth += stream->interval << 3;
         }
-        stream->next_uframe = next_uframe % mod;
+        stream->next_uframe = next_uframe & (mod - 1);
 
         /* don't need that schedule data any more */
         iso_sched_free (stream, sched);
@@ -2258,7 +2258,7 @@ scan_periodic (struct ehci_hcd *ehci)
         now_uframe = ehci->next_uframe;
         if (HC_IS_RUNNING(ehci_to_hcd(ehci)->state)) {
                 clock = ehci_readl(ehci, &ehci->regs->frame_index);
-                clock_frame = (clock >> 3) % ehci->periodic_size;
+                clock_frame = (clock >> 3) & (ehci->periodic_size - 1);
         } else  {
                 clock = now_uframe + mod - 1;
                 clock_frame = -1;
@@ -2267,7 +2267,7 @@ scan_periodic (struct ehci_hcd *ehci)
                 free_cached_lists(ehci);
                 ehci->clock_frame = clock_frame;
         }
-        clock %= mod;
+        clock &= mod - 1;
         clock_frame = clock >> 3;
 
         for (;;) {
@@ -2356,7 +2356,7 @@ restart:
                                  * frame is current.
                                  */
                                 if (((frame == clock_frame) ||
-                                     (((frame + 1) % ehci->periodic_size)
+                                     (((frame + 1) & (ehci->periodic_size - 1))
                                       == clock_frame))
                                     && live
                                     && (q.sitd->hw_results &
@@ -2423,7 +2423,8 @@ restart:
                                         || ehci->periodic_sched == 0)
                                 break;
                         ehci->next_uframe = now_uframe;
-                        now = ehci_readl(ehci, &ehci->regs->frame_index) % mod;
+                        now = ehci_readl(ehci, &ehci->regs->frame_index) &
+                                        (mod - 1);
                         if (now_uframe == now)
                                 break;
 
@@ -2436,7 +2437,7 @@ restart:
                         }
                 } else {
                         now_uframe++;
-                        now_uframe %= mod;
+                        now_uframe &= mod - 1;
                 }
         }
 }