On Tue, 16 May 2006, 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.
Do you have any evidence to back up this suspicion? For example, what happens if you run with 1 channel per PC but with a second USB device (like a flash disk) installed and in use? > 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. Which wMaxPacketSize did you check? Is it the value for endpoint 0 or the value for one of the bulk endpoints? > 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. The kernel's USB stack is already tuned for maximum performance. Alan Stern ------------------------------------------------------- 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
