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USB: EHCI: improve interrupt qh unlink

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ehci-hcd currently unlinks an interrupt QH when it becomes empty, that
is, after its last URB completes.  This works well because in almost
all cases, the completion handler for an interrupt URB resubmits the
URB; therefore the QH doesn't become empty and doesn't get unlinked.

When we start using tasklets for URB completion, this scheme won't work
as well.  The resubmission won't occur until the tasklet runs, which
will be some time after the completion is queued with the tasklet.
During that delay, the QH will be empty and so will be unlinked
unnecessarily.

To prevent this problem, this patch adds a 5-ms time delay before empty
interrupt QHs are unlinked.  Most often, during that time the interrupt
URB will be resubmitted and thus we can avoid unlinking the QH.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ming Lei 2013-07-03 22:53:10 +08:00 • committed by Greg Kroah-Hartman
parent 35371e4fbc
commit 9118f9eb4f
6 changed files with 84 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

34
drivers/usb/host/ehci-timer.c
View file

@ -72,6 +72,7 @@ static unsigned event_delays_ns[] = {
1 * NSEC_PER_MSEC, /* EHCI_HRTIMER_POLL_DEAD */
1125 * NSEC_PER_USEC, /* EHCI_HRTIMER_UNLINK_INTR */
2 * NSEC_PER_MSEC, /* EHCI_HRTIMER_FREE_ITDS */
5 * NSEC_PER_MSEC, /* EHCI_HRTIMER_START_UNLINK_INTR */
6 * NSEC_PER_MSEC, /* EHCI_HRTIMER_ASYNC_UNLINKS */
10 * NSEC_PER_MSEC, /* EHCI_HRTIMER_IAA_WATCHDOG */
10 * NSEC_PER_MSEC, /* EHCI_HRTIMER_DISABLE_PERIODIC */
@ -215,6 +216,36 @@ static void ehci_handle_controller_death(struct ehci_hcd *ehci)
/* Not in process context, so don't try to reset the controller */
}
/* start to unlink interrupt QHs */
static void ehci_handle_start_intr_unlinks(struct ehci_hcd *ehci)
{
bool stopped = (ehci->rh_state < EHCI_RH_RUNNING);
/*
* Process all the QHs on the intr_unlink list that were added
* before the current unlink cycle began. The list is in
* temporal order, so stop when we reach the first entry in the
* current cycle. But if the root hub isn't running then
* process all the QHs on the list.
*/
while (!list_empty(&ehci->intr_unlink_wait)) {
struct ehci_qh *qh;
qh = list_first_entry(&ehci->intr_unlink_wait,
struct ehci_qh, unlink_node);
if (!stopped && (qh->unlink_cycle ==
ehci->intr_unlink_wait_cycle))
break;
list_del_init(&qh->unlink_node);
start_unlink_intr(ehci, qh);
}
/* Handle remaining entries later */
if (!list_empty(&ehci->intr_unlink_wait)) {
ehci_enable_event(ehci, EHCI_HRTIMER_START_UNLINK_INTR, true);
++ehci->intr_unlink_wait_cycle;
}
}
/* Handle unlinked interrupt QHs once they are gone from the hardware */
static void ehci_handle_intr_unlinks(struct ehci_hcd *ehci)
@ -236,7 +267,7 @@ static void ehci_handle_intr_unlinks(struct ehci_hcd *ehci)
unlink_node);
if (!stopped && qh->unlink_cycle == ehci->intr_unlink_cycle)
break;
list_del(&qh->unlink_node);
list_del_init(&qh->unlink_node);
end_unlink_intr(ehci, qh);
}
@ -363,6 +394,7 @@ static void (*event_handlers[])(struct ehci_hcd *) = {
ehci_handle_controller_death, /* EHCI_HRTIMER_POLL_DEAD */
ehci_handle_intr_unlinks, /* EHCI_HRTIMER_UNLINK_INTR */
end_free_itds, /* EHCI_HRTIMER_FREE_ITDS */
ehci_handle_start_intr_unlinks, /* EHCI_HRTIMER_START_UNLINK_INTR */
unlink_empty_async, /* EHCI_HRTIMER_ASYNC_UNLINKS */
ehci_iaa_watchdog, /* EHCI_HRTIMER_IAA_WATCHDOG */
ehci_disable_PSE, /* EHCI_HRTIMER_DISABLE_PERIODIC */