J. Scott Merritt wrote: > Ned wrote: > >> I will try to think about a patch tomorrow. I volunteer to be involved >> in this so that it gets fixed without breaking the other things I need >> to do. Hopefully Stephen will be available to review any patches. > > Thank you for volunterring to work on this. For my particular (embedded) > application, I think that I can get around the problem with an initial > (dummy) transfer to get things set up. ... but I think a general > repair for the Kernel mainline would be a good idea. > > On an unrelated note, I received the message below from someone else > on the SPI list. The issue he raises seems valid based on what I have > seen in my usage ... however, I suspect that a fix would be difficult. > I forward it simply for your information/consideration .... > > Thanks, Scott. > > > While we're on the subject of the pxa2xx_spi driver, I've found that > it's incredibly slow to access. The problem appears to be related to > the use of a tasklet in pumping messages. The initial setup and > transfer is quick but then the tasklet is started and a context switch > causes terrible latency. It takes around a millisecond for the tasklet > to get control at which point the chip select is released and the SPI > bus is available for the next transfer. This means that running as > hard as it can the bus is idle 99% of the time. I've experimented with > removing the tasklet from the driver and it does improve the situation > markedly.
Yes, I have seen this, and have communicated on the list about it. It might be easy to fix, but detrimental to kernel interrupt latency. I would like to hear what Stephen has to say about this, as I know that his application, servicing audio A/Ds and D/As (and for which he wrote the driver), is more typical than my application (a read-only fire hose, streaming 11Mbit/sec data). -- Ned Forrester [EMAIL PROTECTED] Oceanographic Systems Lab 508-289-2226 Applied Ocean Physics and Engineering Dept. Woods Hole Oceanographic Institution Woods Hole, MA 02543, USA http://www.whoi.edu/sbl/liteSite.do?litesiteid=7212 http://www.whoi.edu/hpb/Site.do?id=1532 http://www.whoi.edu/page.do?pid=10079 ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ spi-devel-general mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/spi-devel-general
