3.16.85-rc1 review patch. If anyone has any objections, please let me know.
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From: David Mosberger davidm@egauge.net
commit 98b74b0ee57af1bcb6e8b2e76e707a71c5ef8ec9 upstream.
usb_submit_urb() may take quite long to execute. For example, a single sg list may have 30 or more entries, possibly leading to that many calls to DMA-map pages. This can cause interrupt latency of several hundred micro-seconds.
Avoid the problem by releasing the io->lock spinlock and re-enabling interrupts before calling usb_submit_urb(). This opens races with usb_sg_cancel() and sg_complete(). Handle those races by using usb_block_urb() to stop URBs from being submitted after usb_sg_cancel() or sg_complete() with error.
Note that usb_unlink_urb() is guaranteed to return -ENODEV if !io->urbs[i]->dev and since the -ENODEV case is already handled, we don't have to check for !io->urbs[i]->dev explicitly.
Before this change, reading 512MB from an ext3 filesystem on a USB memory stick showed a throughput of 12 MB/s with about 500 missed deadlines.
With this change, reading the same file gave the same throughput but only one or two missed deadlines.
Signed-off-by: David Mosberger davidm@egauge.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Ben Hutchings ben@decadent.org.uk --- drivers/usb/core/message.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-)
--- a/drivers/usb/core/message.c +++ b/drivers/usb/core/message.c @@ -306,9 +306,10 @@ static void sg_complete(struct urb *urb) */ spin_unlock(&io->lock); for (i = 0, found = 0; i < io->entries; i++) { - if (!io->urbs[i] || !io->urbs[i]->dev) + if (!io->urbs[i]) continue; if (found) { + usb_block_urb(io->urbs[i]); retval = usb_unlink_urb(io->urbs[i]); if (retval != -EINPROGRESS && retval != -ENODEV && @@ -519,12 +520,10 @@ void usb_sg_wait(struct usb_sg_request * int retval;
io->urbs[i]->dev = io->dev; - retval = usb_submit_urb(io->urbs[i], GFP_ATOMIC); - - /* after we submit, let completions or cancellations fire; - * we handshake using io->status. - */ spin_unlock_irq(&io->lock); + + retval = usb_submit_urb(io->urbs[i], GFP_NOIO); + switch (retval) { /* maybe we retrying will recover */ case -ENXIO: /* hc didn't queue this one */ @@ -594,8 +593,8 @@ void usb_sg_cancel(struct usb_sg_request for (i = 0; i < io->entries; i++) { int retval;
- if (!io->urbs[i]->dev) - continue; + usb_block_urb(io->urbs[i]); + retval = usb_unlink_urb(io->urbs[i]); if (retval != -EINPROGRESS && retval != -ENODEV