diff options
| author | David Mosberger <davidm@egauge.net> | 2016-03-09 00:42:48 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-04-27 01:21:41 +0300 |
| commit | 98b74b0ee57af1bcb6e8b2e76e707a71c5ef8ec9 (patch) | |
| tree | e8fd1bbb6cda43e933c304e70d66d7dc91e29791 /drivers/usb/core | |
| parent | 9360575c5837cfee841ad350de5be830b840d972 (diff) | |
| download | linux-98b74b0ee57af1bcb6e8b2e76e707a71c5ef8ec9.tar.xz | |
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 <davidm@egauge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/usb/core')
| -rw-r--r-- | drivers/usb/core/message.c | 15 |
1 files 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 |