From b963801164618e25fbdc0cd452ce49c3628b46c8 Mon Sep 17 00:00:00 2001 From: David Brownell Date: Tue, 3 Jun 2008 22:21:55 -0700 Subject: USB: ehci-hcd unlink speedups This patch fixes some performance bugs observed with some workloads when unlinking EHCI queue header (QH) descriptors from the async ring (control/bulk schedule). The mechanism intended to defer unlinking an empty QH (so there is no penalty in common cases where it's quickly reused) was not working as intended. Sometimes the unlink was scheduled: - too quickly ... which can be a *strong* negative effect, since that QH becomes unavailable for immediate re-use; - too slowly ... wasting DMA cycles, usually a minor issue except for increased bus contention and power usage; Plus there was an extreme case of "too slowly": a logical error in the IAA watchdog-timer conversion meant that sometimes the unlink never got scheduled. The fix replaces a simple counter with a timestamp derived from the controller's 8 KHz microframe counter, and adjusts the timer usage for some issues associated with HZ being less than 8K. (Based on a patch originally by Alan Stern, and good troubleshooting from Leonid.) Signed-off-by: David Brownell Cc: Alan Stern Cc: Leonid Signed-off-by: Greg Kroah-Hartman --- drivers/usb/host/ehci-q.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) (limited to 'drivers/usb/host/ehci-q.c') diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c index b85b54160cda..2622b6596d7c 100644 --- a/drivers/usb/host/ehci-q.c +++ b/drivers/usb/host/ehci-q.c @@ -1116,8 +1116,7 @@ static void scan_async (struct ehci_hcd *ehci) struct ehci_qh *qh; enum ehci_timer_action action = TIMER_IO_WATCHDOG; - if (!++(ehci->stamp)) - ehci->stamp++; + ehci->stamp = ehci_readl(ehci, &ehci->regs->frame_index); timer_action_done (ehci, TIMER_ASYNC_SHRINK); rescan: qh = ehci->async->qh_next.qh; @@ -1142,18 +1141,20 @@ rescan: } } - /* unlink idle entries, reducing HC PCI usage as well + /* unlink idle entries, reducing DMA usage as well * as HCD schedule-scanning costs. delay for any qh * we just scanned, there's a not-unusual case that it * doesn't stay idle for long. * (plus, avoids some kind of re-activation race.) */ - if (list_empty (&qh->qtd_list)) { - if (qh->stamp == ehci->stamp) + if (list_empty(&qh->qtd_list) + && qh->qh_state == QH_STATE_LINKED) { + if (!ehci->reclaim + && ((ehci->stamp - qh->stamp) & 0x1fff) + >= (EHCI_SHRINK_FRAMES * 8)) + start_unlink_async(ehci, qh); + else action = TIMER_ASYNC_SHRINK; - else if (!ehci->reclaim - && qh->qh_state == QH_STATE_LINKED) - start_unlink_async (ehci, qh); } qh = qh->qh_next.qh; -- cgit v1.2.3