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@xxxxxxxxxxxxxxxxxxx>
CC: David Brownell <david-b@xxxxxxxxxxx>
---
Index: usb-2.6/drivers/usb/host/ehci-sched.c
===================================================================
--- usb-2.6.orig/drivers/usb/host/ehci-sched.c
+++ usb-2.6/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;
}
}
}
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