On Wed, 31 Oct 2012, Paul Zimmerman wrote: > > From: Michal Nazarewicz [mailto:mpn@xxxxxxxxxx] On Behalf Of Michal Nazarewicz > > Sent: Wednesday, October 31, 2012 1:10 PM > > > > On Wed, Oct 31 2012, Paul Zimmerman wrote: > > > Regarding that, would you guys accept a patch that adds the "buflen" > > > module parameter to the mass-storage gadget? Without increasing the > > > buffer length above 16K, it's impossible to approach the max throughput > > > allowed by SuperSpeed hosts. > > > > I have no problem with that. But did you try setting up 4 buffers? you > > can set number of buffers g_{file,mass}_storage uses with config > > USB_GADGET_STORAGE_NUM_BUFFERS (or if you select USB_GADGET_DEBUG_FILES > > you get a fsg_num_buffers module parameter). > > Yeah, I tried that, but it didn't have much effect. Whereas increasing num_buffers > to 4 and buffer length to 128K gives a large improvement, from less than 200 MB/s > to about 290 MB/s. No doubt this is a matter of interrupt latency. I don't know the maximum throughput for SuperSpeed bulk data, so I'll guess it's about 8 times that of high speed (500 MB/s vs. 480 Mb/s). High speed bulk data can be transferred at rates up to 6.5 KB/uframe (although the values one sees in practice are almost never that high). This means SuperSpeed bulk data can be transferred at rates up to 52 KB/uframe. Assuming we get completion interrupts only at microframe boundaries, bulk data buffers should be at least 64 KB, and preferably larger. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
