On Fri, Oct 29, 2004, Duncan Sands <[EMAIL PROTECTED]> wrote: > On Friday 29 October 2004 18:50, Johannes Erdfelt wrote: > > On Fri, Oct 29, 2004, Duncan Sands <[EMAIL PROTECTED]> wrote: > > > Hi Johannes, maybe it should allocate multiple pages and then use scatter-gather > > > io out of them. That avoids having to allocate large contiguous lumps of kernel > > > memory, and should also be good for performance. > > > > Are you talking about exporting scatter-gather via usbfs? Or having the > > kernel avoid a copy from userspace by using scatter-gather internally? > > > > The former might be useful, but only if the application really goes out > > of the way to use it. > > > > The latter sounds good, but might be tricky. Scatter-gather implies > > properly sized buffers to ensure the correct packetization, which I > > don't think userspace could guarantee. > > Neither! Right now usbfs allocates a buffer (max size: 16k), and copies > the data from user-space. The problem is that this requires finding > several contiguous pages of kernel memory (max: 5 pages). I'm worried about > memory pressure here. If usbfs instead grabbed a bunch of non-contiguous > pages, copied the data into them from user-space, and then sent it (using > scatter-gather io), then there is no longer any memory pressure problem. > What's more, there would also be no reason not to increase the maximum > data size from 16k to something much bigger, say 256k. Allowing bigger > buffers should increase performance.
Duh, that would be the obvious way to increase performance and reliability. Not to mention it should be relatively easy to implement. JE ------------------------------------------------------- This SF.Net email is sponsored by: Sybase ASE Linux Express Edition - download now for FREE LinuxWorld Reader's Choice Award Winner for best database on Linux. http://ads.osdn.com/?ad_id=5588&alloc_id=12065&op=click _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
