Low perfomance when read from usb flash drive

Steve Calfee stevecalfee at gmail.com
Wed Mar 4 14:37:59 PST 2009

On Wed, Mar 4, 2009 at 2:10 PM, Hans Petter Selasky <hselasky at c2i.net> wrote:
> On Wednesday 04 March 2009, Artyom Mirgorodsky wrote:
>> I forgot to write, that a similar problem was observed in FreeBSD 7 with
>> usb4bsd patches.
> Here is a patch which I think will address your problem. It is EHCI hardware
> related. Different models behave differently. Try this:
> http://perforce.freebsd.org/chv.cgi?CH=158692

Wow, that is bizarre. The "doorbell" is usually used so the software
knows that the cpu vs dma race is complete when moving qtds off the qh
- ie dequeueing requests. What you have done is asked the guy doing
the photo finish at the end of a horse race to press the shutter a
little before the horse crosses the line - so the shutter latency will
allow a picture right as the horse crosses the line. Unfortunately,
this (like all races) is affected by the object doing the racing -
horse speed and camera speed are variable!

I believe something else must be wrong.

Regards, Steve

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