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b963801164
This patch fixes some performance bugs observed with some workloads when unlinking EHCI queue header (QH) descriptors from the async ring (control/bulk schedule). The mechanism intended to defer unlinking an empty QH (so there is no penalty in common cases where it's quickly reused) was not working as intended. Sometimes the unlink was scheduled: - too quickly ... which can be a *strong* negative effect, since that QH becomes unavailable for immediate re-use; - too slowly ... wasting DMA cycles, usually a minor issue except for increased bus contention and power usage; Plus there was an extreme case of "too slowly": a logical error in the IAA watchdog-timer conversion meant that sometimes the unlink never got scheduled. The fix replaces a simple counter with a timestamp derived from the controller's 8 KHz microframe counter, and adjusts the timer usage for some issues associated with HZ being less than 8K. (Based on a patch originally by Alan Stern, and good troubleshooting from Leonid.) Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> Cc: Alan Stern <stern@rowland.harvard.edu> Cc: Leonid <leonidv11@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
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| usb-skeleton.c | ||
To understand all the Linux-USB framework, you'll use these resources:
* This source code. This is necessarily an evolving work, and
includes kerneldoc that should help you get a current overview.
("make pdfdocs", and then look at "usb.pdf" for host side and
"gadget.pdf" for peripheral side.) Also, Documentation/usb has
more information.
* The USB 2.0 specification (from www.usb.org), with supplements
such as those for USB OTG and the various device classes.
The USB specification has a good overview chapter, and USB
peripherals conform to the widely known "Chapter 9".
* Chip specifications for USB controllers. Examples include
host controllers (on PCs, servers, and more); peripheral
controllers (in devices with Linux firmware, like printers or
cell phones); and hard-wired peripherals like Ethernet adapters.
* Specifications for other protocols implemented by USB peripheral
functions. Some are vendor-specific; others are vendor-neutral
but just standardized outside of the www.usb.org team.
Here is a list of what each subdirectory here is, and what is contained in
them.
core/ - This is for the core USB host code, including the
usbfs files and the hub class driver ("khubd").
host/ - This is for USB host controller drivers. This
includes UHCI, OHCI, EHCI, and others that might
be used with more specialized "embedded" systems.
gadget/ - This is for USB peripheral controller drivers and
the various gadget drivers which talk to them.
Individual USB driver directories. A new driver should be added to the
first subdirectory in the list below that it fits into.
image/ - This is for still image drivers, like scanners or
digital cameras.
../input/ - This is for any driver that uses the input subsystem,
like keyboard, mice, touchscreens, tablets, etc.
../media/ - This is for multimedia drivers, like video cameras,
radios, and any other drivers that talk to the v4l
subsystem.
../net/ - This is for network drivers.
serial/ - This is for USB to serial drivers.
storage/ - This is for USB mass-storage drivers.
class/ - This is for all USB device drivers that do not fit
into any of the above categories, and work for a range
of USB Class specified devices.
misc/ - This is for all USB device drivers that do not fit
into any of the above categories.