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| author | Alan Stern <stern@rowland.harvard.edu> | 2008-05-20 20:59:33 (GMT) |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2008-05-29 20:59:04 (GMT) |
| commit | fa38dfcc56b5f6cce787f9aaa5d1830509213802 (patch) | |
| tree | af6c68e248233434cce1b8a4bcf361039aa5ef8f /drivers | |
| parent | b40e43fcc532fa44a375a37d592e32cd0d50fe7a (diff) | |
| download | linux-fa38dfcc56b5f6cce787f9aaa5d1830509213802.tar.xz | |
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')
| -rw-r--r-- | drivers/usb/host/ehci-hcd.c | 3 | ||||
| -rw-r--r-- | drivers/usb/host/ehci-q.c | 15 |
2 files changed, 10 insertions, 8 deletions
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 @@ 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 b85b541..5200481 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; |