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USB: EHCI: start new isochronous streams ASAP

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This patch changes the initial delay before the startup of a newly
scheduled isochronous stream.  Currently the stream doesn't start
for at least 5 ms (40 microframes).  This value is just an estimate;
it has no real justification.

Instead, we can start the stream as soon as possible after the
scheduling computations are complete.  Essentially this requires
nothing more than reading the frame counter after the stream is
scheduled, instead of before.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alan Stern 2013-10-11 11:29:36 -04:00 committed by Greg Kroah-Hartman
parent b35c5009bb
commit a393a807d0
1 changed files with 23 additions and 21 deletions
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44
drivers/usb/host/ehci-sched.c
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@ -1491,8 +1491,6 @@ sitd_slot_ok (
* given EHCI_TUNE_FLS and the slop). Or, write a smarter scheduler!
*/
#define SCHEDULING_DELAY 40 /* microframes */
static int
iso_stream_schedule (
struct ehci_hcd *ehci,
@ -1506,27 +1504,13 @@ iso_stream_schedule (
unsigned mod = ehci->periodic_size << 3;
struct ehci_iso_sched *sched = urb->hcpriv;
bool empty = list_empty(&stream->td_list);
bool new_stream = false;
period = stream->uperiod;
span = sched->span;
if (!stream->highspeed)
span <<= 3;
now = ehci_read_frame_index(ehci) & (mod - 1);
/* Take the isochronous scheduling threshold into account */
if (ehci->i_thresh)
next = now + ehci->i_thresh; /* uframe cache */
else
next = (now + 2 + 7) & ~0x07; /* full frame cache */
/*
* Use ehci->last_iso_frame as the base. There can't be any
* TDs scheduled for earlier than that.
*/
base = ehci->last_iso_frame << 3;
next = (next - base) & (mod - 1);
/* Start a new isochronous stream? */
if (unlikely(empty && !hcd_periodic_completion_in_progress(
ehci_to_hcd(ehci), urb->ep))) {
@ -1542,7 +1526,7 @@ iso_stream_schedule (
}
compute_tt_budget(ehci->tt_budget, tt);
start = (now & ~0x07) + SCHEDULING_DELAY;
start = ((-(++ehci->random_frame)) << 3) & (period - 1);
/* find a uframe slot with enough bandwidth.
* Early uframes are more precious because full-speed
@ -1585,17 +1569,35 @@ iso_stream_schedule (
start = (stream->ps.phase << 3) + stream->ps.phase_uf;
}
start = (start - base) & (mod - 1);
goto use_start;
stream->next_uframe = start;
new_stream = true;
}
now = ehci_read_frame_index(ehci) & (mod - 1);
/* Take the isochronous scheduling threshold into account */
if (ehci->i_thresh)
next = now + ehci->i_thresh; /* uframe cache */
else
next = (now + 2 + 7) & ~0x07; /* full frame cache */
/*
* Use ehci->last_iso_frame as the base. There can't be any
* TDs scheduled for earlier than that.
*/
base = ehci->last_iso_frame << 3;
next = (next - base) & (mod - 1);
start = (stream->next_uframe - base) & (mod - 1);
if (unlikely(new_stream))
goto do_ASAP;
/*
* Typical case: reuse current schedule, stream may still be active.
* Hopefully there are no gaps from the host falling behind
* (irq delays etc). If there are, the behavior depends on
* whether URB_ISO_ASAP is set.
*/
start = (stream->next_uframe - base) & (mod - 1);
now2 = (now - base) & (mod - 1);
/* Is the schedule already full? */