path: root/drivers/usb/host/ehci-sched.c
diff options
authorAlan Stern <stern@rowland.harvard.edu>2011-05-17 10:40:51 -0400
committerGreg Kroah-Hartman <gregkh@suse.de>2011-05-17 11:20:24 -0700
commit1e12c910eed82da6971f1c0421a069c680faba2e (patch)
tree46851229d59c72fa10596f7cecd567918ce348eb /drivers/usb/host/ehci-sched.c
parent2b7aaf503d56216b847c8265421d2a7d9b42df3e (diff)
EHCI: don't rescan interrupt QHs needlessly
This patch (as1466) speeds up processing of ehci-hcd's periodic list. The existing code will pointlessly rescan an interrupt endpoint queue each time it encounters the queue's QH in the periodic list, which can happen quite a few times if the endpoint's period is low. On some embedded systems, this useless overhead can waste so much time that the driver falls hopelessly behind and loses events. The patch introduces a "periodic_stamp" variable, which gets incremented each time scan_periodic() runs and each time the scan advances to a new frame. If the corresponding stamp in an interrupt QH is equal to the current periodic_stamp, we assume the QH has already been scanned and skip over it. Otherwise we scan the QH as usual, and if none of its URBs have completed then we store the current periodic_stamp in the QH's stamp, preventing it from being scanned again. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'drivers/usb/host/ehci-sched.c')
1 files changed, 10 insertions, 4 deletions
diff --git a/drivers/usb/host/ehci-sched.c b/drivers/usb/host/ehci-sched.c
index 1543c838b3d1..a7408d88fda0 100644
--- a/drivers/usb/host/ehci-sched.c
+++ b/drivers/usb/host/ehci-sched.c
@@ -2287,6 +2287,7 @@ scan_periodic (struct ehci_hcd *ehci)
clock &= mod - 1;
clock_frame = clock >> 3;
+ ++ehci->periodic_stamp;
for (;;) {
union ehci_shadow q, *q_p;
@@ -2315,10 +2316,14 @@ restart:
temp.qh = qh_get (q.qh);
type = Q_NEXT_TYPE(ehci, q.qh->hw->hw_next);
q = q.qh->qh_next;
- modified = qh_completions (ehci, temp.qh);
- if (unlikely(list_empty(&temp.qh->qtd_list) ||
- temp.qh->needs_rescan))
- intr_deschedule (ehci, temp.qh);
+ if (temp.qh->stamp != ehci->periodic_stamp) {
+ modified = qh_completions(ehci, temp.qh);
+ if (!modified)
+ temp.qh->stamp = ehci->periodic_stamp;
+ if (unlikely(list_empty(&temp.qh->qtd_list) ||
+ temp.qh->needs_rescan))
+ intr_deschedule(ehci, temp.qh);
+ }
qh_put (temp.qh);
@@ -2460,6 +2465,7 @@ restart:
if (ehci->clock_frame != clock_frame) {
ehci->clock_frame = clock_frame;
+ ++ehci->periodic_stamp;
} else {