Date: Thu, 2 Dec 1999 08:43:19 -0800 (PST) From: Nick Hibma <n_hibma@FreeBSD.org> To: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: cvs commit: src/sys/dev/usb uhci.c Message-ID: <199912021643.IAA11449@freefall.freebsd.org>
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n_hibma 1999/12/02 08:43:19 PST
Modified files:
sys/dev/usb uhci.c
Log:
In one queue all the TDs (transfer descriptor, packets) for one transfer
are queued. Traverse the queues vertically and then horizontally.
This means that TDs for one xfer are transmitted back to back until the
first NAK or error condition. Up to now we transmitted a TD per frame
and transmitted the next TD in the next frame.
The old approach is more fair if you have the end of the queue point at
the beginning of the control transfer queue, but also a lot more overhead
due to the fact that the QHs have to be read more often.
The new approach squirts the packets down the line as fast as possible
for one transfer and then does the next one. In the current situation,
with fairly empty USB buses, this is a more sensible approach. We might
have to revisit the scheduler later however.
It speeds up large transfers (Zip drive, Host-To-Host adapters) on UHCI
by a factor of 5 and makes it as fast as OHCI on the bus.
The next problem to solve is the question why the limit is 300kb/s and
not 1000/kb/s (kb == kilobyte).
Revision Changes Path
1.35 +7 -4 src/sys/dev/usb/uhci.c
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