On Sat, 28 Sep 2013, Ming Lei wrote: > On Wed, Sep 25, 2013 at 3:12 AM, Markus Rechberger > <mrechberger@xxxxxxxxx> wrote: > > This patch adds memory mapping support to USBFS for isochronous and bulk > > data transfers, it allows to pre-allocate usb transfer buffers. > > > > The CPU usage decreases 1-2% on my 1.3ghz U7300 notebook when > > transferring 20mbyte/sec, it should be more interesting to see those > > statistics on embedded systems where copying data is more expensive. > > Given USB3 is becoming popular and throughput is increased much, zero > copy should be charming. > > And another approach is to use direct I/O method(SG DMA to pages > allocated to user space directly), which should be more flexible, and > user don't need to use mmap/munmap, so should be easier to use. > > At least, wrt. usb mass storage test, both CPU utilization and throughput > can be improved with direct I/O. For zero-copy to work, on many systems the pages have to be allocated in the first 4 GB of physical memory. How can the userspace program make sure this will happen? 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
