From a393a807d0c805e7c723315ff0e88a857055e9c6 Mon Sep 17 00:00:00 2001 From: Alan Stern Date: Fri, 11 Oct 2013 11:29:36 -0400 Subject: [PATCH] USB: EHCI: start new isochronous streams ASAP 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 Signed-off-by: Greg Kroah-Hartman --- drivers/usb/host/ehci-sched.c | 44 ++++++++++++++++++++++--------------------- 1 file changed, 23 insertions(+), 21 deletions(-) diff --git a/drivers/usb/host/ehci-sched.c b/drivers/usb/host/ehci-sched.c index b5f957d..7ce5c2a 100644 --- a/drivers/usb/host/ehci-sched.c +++ b/drivers/usb/host/ehci-sched.c @@ -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? */ -- 2.7.4