It depends on the driver implementation, ie. if the kernel code is using preempt disable or disable interrupts.
ALL preempt-rt performance is to a large extent dependent on the quality of the device drivers. If you look at osadl.org there is an effort on realtime device drivers ... / Lars 2014-01-30 Michael Haberler <mai...@mah.priv.at>: > 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 ------------------------------------------------------------------------------ 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
