On Thu, 19 Jun 2003, Major A wrote: > > > About possible performance improvement on 2.5 ehci/usb-storage: > > > I've tested with 2.5.71, and I don't see a significant improvement over 2.4. > > > (Both are arround 7.7 MB/s for read, 10 MB/s for write). Disk can do arround > > > 40 MB/s reads on IDE. > > > > I don't know what's going on there. > > I'm seeing the same speed here as well, and the disk can certainly do > more than 10MB/s sustained. I'm using the same USB-IDE bridge > (Genesys). > > I'm not familiar with the way USB storage devices work, but I guess > you tell the disk to read from a certain location using a bulk OUT > transfer, then request a series of bulk INs to obtain the data. Since > INs are handled in a very funny way in USB (the data has to be there > already, otherwise the host gets a NAK), I wouldn't be surprised if > the USB-IDE bridge was at least part of the bottleneck here. Writes > are less problematic -- you just dump the data in bulk OUT packets and > the bridge writes to IDE whatever it can whenever it can.
I agree it's quite likely that the USB-IDE bridge is part of the bottleneck. But USB itself shouldn't be that much of a limiting factor. The raw speed of the bus is around 60 MB/sec, and even with all the overhead you should still be able to get half that (I think) on an unloaded system. Bulk data transfers from USB mass storage devices are very straightforward; what happens is that device NAKs repeatedly until the data is ready, at which point it transfers the data. The data doesn't even have to be all there, just enough to fill up the next packet. There's nothing very funny about it -- in fact, in would _really_ be funny if the device could transmit the data _before_ it was there! :-) Alan Stern ------------------------------------------------------- This SF.Net email is sponsored by: INetU Attention Web Developers & Consultants: Become An INetU Hosting Partner. Refer Dedicated Servers. We Manage Them. You Get 10% Monthly Commission! INetU Dedicated Managed Hosting http://www.inetu.net/partner/index.php _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
