On Tue, May 16, 2006 at 09:27:22AM -0700, Adisorn Ermongkonchai wrote: > Hi, > > First of, I am very new to USB. My project is wireless related (not > USB) and I am in the process of testing the Linux (kernel 2.6.16.15) > wireless performance using wireless usb devices. I use D-Link USB > (54Mbps) device as my testing device. The max performance of wireless > transmission is roughly around 25Mbps. I am currently using > 2 wireless channels (chan 6 and 11) without encryption. My tests > are as followed. > > Using 4 PCs called PC1, PC2, PC3, and PC4, PC1 and PC2 > are connected with each other in Ad-Hoc mode channel 6. > PC3 and PC4 are connected using channel 11 also Adhoc mode. > The performance is as expected. Each pair is transmitted at > expected speed around 20-25Mbps. I use "ttcp" to test its speed. > This test is to ensure that channel 6 and 11 do not interfere with > each other and they seemed that they do not interfere with each > other. > > But when I used 2 PC's with 2 channels per PC. again in > Adhoc mode and ran ttcp on both channels simultaneously, > the speed of each channel went down by 1/3 to 1/2 of the > expected speed. I suspect that it is USB related.
Why? Isn't this expected behavior based on how the wireless network protocol works? > BTW, I don't have any other devices running on the USB port, > just the 2 wireless USBs. > > So I dig into the D-link USB driver (open source by Ralink) and > found that it uses Bulk transfer mode. And the code seems to > be reasonable. It calls "usb_fill_bulk_urb" with "usb_sndbulkpipe" > and "complete" callback function and then calls "usb_submit_urb" > to do the transmit. When "complete" callback is called, the > transmit procedure is repeated if there are still packets in the > queue. > > I check the "wMaxPacketSize", it is already set to 64 when the > probe function is called. Is there anything that I could do to > enhance the performance. Why not ask the authors of the driver about this? They would be the best ones to know if increasing the size of the urb would cause any problems or not. > BTW, I don't have USB analyzer to look at the USB bus. Any > suggestions are appreciated. Hopefully, there is some place > that I could tweak in the kernel to improve the performance. You might invest in some good tools to try to track down performance problems. The problem might not be in the USB code at all. good luck, greg k-h ------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
