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>
diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index 369a8a5..3e3c5d3 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -84,7 +84,8 @@
#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 b85b541..5200481 100644
--- a/drivers/usb/host/ehci-q.c
+++ b/drivers/usb/host/ehci-q.c
@@ -1116,8 +1116,7 @@
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 @@
* 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;