On Mon, 5 Oct 2015, Alan Stern wrote: > On Mon, 5 Oct 2015, Paul Jones wrote: > >>> Increasing the max_sectors_kb value, on the other hand, might remove >>> overhead by allowing a higher percentage of the transfer to consist of >>> real data as opposed to CBW and CSW packets. This depends to some >>> extent on other factors (such as whether the memory pages are >>> contiguous, allowing for larger transfers), but it can't hurt. >> >> I tried changing the max_sectors_kb to 64 with 64k block size in dd and it’s transferring at the same \ > speed. > > That's a decrease, not an increase. Try changing it to 1024 or more. > >> I verified using usbmon and it then indeed requests 64k in each request. >> Increasing the dd block size to 240k doesn’t change the transfer speed either, and it keeps using \ >> alternating 120k/8k requests. Increasing the dd block size to 1M doesn’t change the transfer speed \ >> either, although I get sequences of 2x 120k followed by 1x 16k requests. > > The dd block size makes no difference at all, because the kernel > aggregates the requests from dd. In my experience, you need to do at least the following to get max performance from the mass storage gadget: - Use Windows 8 or higher on the host. It's much faster than Linux. - Put the backing file for the mass storage gadget on a tmpfs. - Increase FSG_BUFLEN (in drivers/usb/gadget/function/storage_common.h) to at least 128K. -- Paul -- 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
