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authorAlan Stern <stern@rowland.harvard.edu>2008-05-20 16:59:33 -0400
committerGreg Kroah-Hartman <gregkh@suse.de>2008-05-29 13:59:04 -0700
commitfa38dfcc56b5f6cce787f9aaa5d1830509213802 (patch)
treeaf6c68e248233434cce1b8a4bcf361039aa5ef8f /drivers/usb
parentb40e43fcc532fa44a375a37d592e32cd0d50fe7a (diff)
USB: EHCI: fix performance regression
This patch (as1099) fixes a performance regression in ehci-hcd. The fundamental problem is that queue headers get removed from the schedule too quickly, since the code checks for a counter advancing rather than making an actual time-based check. The latency involved in removing the queue header and then relinking it can severely degrade certain kinds of workloads. The patch replaces a simple counter with a timestamp derived from the controller's uframe value. In addition, the delay for unlinking an idle queue header is increased from 5 ms to 10 ms; since some controllers (nVidia) have a latency of up to 1 ms for unlinking, this reduces the relative impact from 20% to 10%. Finally, a logical error left over from the IAA watchdog-timer conversion is corrected. Now the driver will always either unlink an idle queue header or set up a timer to unlink it later. The old code would sometimes fail to do either. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Cc: David Brownell <david-b@pacbell.net> Cc: Leonid <leonidv11@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'drivers/usb')
-rw-r--r--drivers/usb/host/ehci-hcd.c3
-rw-r--r--drivers/usb/host/ehci-q.c15
2 files changed, 10 insertions, 8 deletions
diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index 369a8a5ea7b..3e3c5d3ea0a 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -84,7 +84,8 @@ static const char hcd_name [] = "ehci_hcd";
#define EHCI_IAA_MSECS 10 /* arbitrary */
#define EHCI_IO_JIFFIES (HZ/10) /* io watchdog > irq_thresh */
#define EHCI_ASYNC_JIFFIES (HZ/20) /* async idle timeout */
-#define EHCI_SHRINK_JIFFIES (HZ/200) /* async qh unlink delay */
+#define EHCI_SHRINK_JIFFIES (HZ/100) /* async qh unlink delay */
+#define EHCI_SHRINK_UFRAMES (10*8) /* same value in uframes */
/* Initial IRQ latency: faster than hw default */
static int log2_irq_thresh = 0; // 0 to 6
diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c
index b85b54160cd..5200481deb2 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;
@@ -1148,12 +1147,14 @@ rescan:
* 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) & 8191) >=
+ EHCI_SHRINK_UFRAMES)
+ 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;