On Tue, 27 Mar 2007 13:40:23 -0700, David Brownell <[EMAIL PROTECTED]> wrote:
> Actually, HID was one of the original motivations for using that. > Dave Miller noticed the cost for a USB keyboard was excessive on > (ISTR) SPARC64, and avoiding all those cache ops was a Good Thing. Are you sure that you're not confusing this with the DMA pool? I'll poke Dave about it, thanks for the hint. > ISTR that isochronous transfers were discussed as potentially a > good use of those no-cache-ops buffers. Hmm... A CPU has to access all that data, and reading a cache line at a time surely as better. Although on the other hand, it's something streaming and thus just using the cache space for no good reason. > It's not clear to me that serial lines would be inappropriate; > what guideline are you thinking of, to suggest they would be? I thought in terms of the exchange sitting there for extended periods of time. This would say that HID is better to be served uncached, and also its I/O sizes are miniscule... As far as performance is concerned, sometimes it is cheaper to use uncached memory, for example sunlance does it on purpose. In case of Oliver's patch, he fixed a bug where exchanges did not end on a cache line boundary, so that's great. Also, the kmalloc size was too big, so replacing a 2D matrix with a vector of pointers was good too. His patch was correct, as far as I can tell. It just seemed to me that in case when we do not know the benefits, we might as well use kmalloc. OK... I admit I must do something for usbmon working better when DMA is pre-allocated, especially on PPC (where it simply gives up immediately and returns 'D' tag). But it's somewhat difficult. There's no portable API which I could use. -- Pete ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
