From 98b74b0ee57af1bcb6e8b2e76e707a71c5ef8ec9 Mon Sep 17 00:00:00 2001 From: David Mosberger Date: Tue, 8 Mar 2016 14:42:48 -0700 Subject: [PATCH] drivers: usb: core: Don't disable irqs in usb_sg_wait() during URB submit. 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 Signed-off-by: Greg Kroah-Hartman --- drivers/usb/core/message.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c index 8e641b5893ed..e13a2e557715 100644 --- a/drivers/usb/core/message.c +++ b/drivers/usb/core/message.c @@ -302,9 +302,10 @@ 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 && @@ -515,12 +516,10 @@ void usb_sg_wait(struct usb_sg_request *io) 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 */ @@ -590,8 +589,8 @@ void usb_sg_cancel(struct usb_sg_request *io) 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