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. 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
