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From 1729d20333739e6cc23023e405fe8668f08117a2 Mon Sep 17 00:00:00 2001
From: Alan Stern <stern@rowland.harvard.edu>
Date: Tue, 17 May 2011 10:40:51 -0400
Subject: [PATCH 1/2] 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>
---
drivers/usb/host/ehci-q.c | 1 +
drivers/usb/host/ehci-sched.c | 14 ++++++++++----
drivers/usb/host/ehci.h | 1 +
3 files changed, 12 insertions(+), 4 deletions(-)
diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c
index ed8db6a..0079610 100644
--- a/drivers/usb/host/ehci-q.c
+++ b/drivers/usb/host/ehci-q.c
@@ -826,6 +826,7 @@ qh_make (
is_input, 0,
hb_mult(maxp) * max_packet(maxp)));
qh->start = NO_FRAME;
+ qh->stamp = ehci->periodic_stamp;
if (urb->dev->speed == USB_SPEED_HIGH) {
qh->c_usecs = 0;
diff --git a/drivers/usb/host/ehci-sched.c b/drivers/usb/host/ehci-sched.c
index a530856..9e54e85 100644
--- a/drivers/usb/host/ehci-sched.c
+++ b/drivers/usb/host/ehci-sched.c
@@ -2351,6 +2351,7 @@ scan_periodic (struct ehci_hcd *ehci)
}
clock %= mod;
clock_frame = clock >> 3;
+ ++ehci->periodic_stamp;
for (;;) {
union ehci_shadow q, *q_p;
@@ -2379,10 +2380,14 @@ 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);
break;
case Q_TYPE_FSTN:
@@ -2515,6 +2520,7 @@ restart:
if (ehci->clock_frame != clock_frame) {
free_cached_lists(ehci);
ehci->clock_frame = clock_frame;
+ ++ehci->periodic_stamp;
}
} else {
now_uframe++;
diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
index c702e4b..c2c2f9d 100644
--- a/drivers/usb/host/ehci.h
+++ b/drivers/usb/host/ehci.h
@@ -117,6 +117,7 @@ struct ehci_hcd { /* one per controller */
struct timer_list watchdog;
unsigned long actions;
unsigned stamp;
+ unsigned periodic_stamp;
unsigned random_frame;
unsigned long next_statechange;
ktime_t last_periodic_enable;
--
1.7.6
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