On Mon, Jan 13, 2014 at 9:26 PM, David Laight <david.lai...@aculab.com> wrote: >> >> I believe all processing use the urb->num_sgs field to limit the number >> of entries. Common interfaces like dma_map_sg() and for_each_sg() limit >> their processing to "nents" entries, and the USB code use the value of >> urb->num_sgs for this parameter. > > Which mostly means that the sg_xxx functions are doing a whole load > of unnecessary instructions and memory accesses... > > This probably has a lot to do with the significant difference in the > cpu use for the usb3 and 'normal' ethernet interfaces. > > While each bit doesn't seem significant, they soon add up.
If you plan to remove the 'nents' parameter, I am wondering if it is a good idea, because sg_nents() should be more heavy. Not mention sometimes the callers just want to map/unmap part of entries. Thanks, -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
