[BRLTTY] -b auto -d usb:

[Mario Lang]

Hi.

Our current implementation of -b auto on the USB bus
does work, but it is pretty inefficient.  This gets extremely
obvious if one tries to run brltty in auto-detection mode
on a small embeeded-type device, like ARM based machines
running Linux.  While BRLTTY is idling and trying to
find a braille display, it consumes a lot of CPU time.

Even on not so small systems you can notice the performance
hit.  On a 2.8GHz machine of mine, brltty consumes 4% cpu
every few seconds when watched with top.

This is because we are iterating the whole USB for every
single driver that supports USB devices.
Can we think of a way to collect relevant USB IDs in autodetection
mode beforehand, and do the iterating just once?  Alternatively, can
we perhaps cache USB device tree information during a cycle
of driver open attempts?

-- 
CYa,
  Mario | Debian Developer <URL:http://debian.org/>
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