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>

diff --git a/drivers/usb/host/ehci-sched.c b/drivers/usb/host/ehci-sched.c
index efadced..27dd841 100644 (file)
--- 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;
                }
        }
 }