Michal is trying hard to get the 7i80/hm2_eth.c driver working for RT-PREEMPT using normal socket I/O from an RT thread.
The hopes with RT-PREEMPT are obviously pegged on the assumption: 'the kernel is hardened, so I'm free to use any system calls from an RT thread and still get decent latency, so we can leverage of the stock linux driver universe'. This might not be a valid assumption. I just had a long offline discussion with Nicholas Mc Guire from the rt-preempt effort on a related issue (signaling a non-RT thread from an RT thread; the method I proposed uses a write(2) system call on an eventfd(2) file descriptor; one of the most efficient ways to signal a poll(2) compatible event between threads). Nicholas pointed me to the fact that almost all system system calls might be spoilers for RT threads; _including write(2)_ , hardened kernel or not. While I didnt fully understand every detail he said, the message was clear: the above assumption might not hold. He also pointed at that hoping for low latency when using the kernel IP stack may be a lost cause to start with. He hinted towards a UIO-based userland stack being worked on for exactly this purpose. I am still searching for details on this. My recommendation is: peer-review your assumptions to avoid a time waster here. Get in touch with linux-rt-us...@vger.kernel.org, describe what you intend, get advice straight from the people who make it happen. - Michael -- ps: IMV the search for a low-latency network I/O method is still on. Note that we already have a userland PCI framework thanks to Charles, which might be a startng point. See also: http://static.mah.priv.at/public/rtlws-proceedings/rtlws-2012/proc/Yang.pdf http://os.inf.tu-dresden.de/ddekit/dde_rtlws11.pdf. semi-related: anyone looking into RT-PREEMPT on ARM CPU's should read: http://lwn.net/images/conf/rtlws11/papers/proc/p11.pdf ------------------------------------------------------------------------------ WatchGuard Dimension instantly turns raw network data into actionable security intelligence. It gives you real-time visual feedback on key security issues and trends. Skip the complicated setup - simply import a virtual appliance and go from zero to informed in seconds. http://pubads.g.doubleclick.net/gampad/clk?id=123612991&iu=/4140/ostg.clktrk _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers