Ish Rattan wrote: > On Tue, 5 Feb 2002, Tyson D Sawyer wrote: > > >>Ish Rattan wrote: >> >> >>>On Mon, 4 Feb 2002, Saikrishnan Krishnamurthy wrote: >>> >>> >>> >>>> 1) Is there any means in linux kernel to offer a kernel thread, a >>>>real-time priority. (I tried assigning the SCHED_RR and SCHED_FIFO to my >>>>threads and it would hang my computer not measuring anythin >>>> >>>> >>>Linux kernel has no notion of real-time and hence priority. >>> >> >>Uhh... are you smoking crack? >> > Using this type of language does not help.
Misinformation that RTLinux and BlueCat linux both seem to spread doesn't help either. Its as if these two groups are trying too hard to prove that they are needed by spreading misinformation when it isn't needed. Hard realtime with uS latencies can't be done by the standard kernel so they are needed and always will be. However, spreading misinformation about what the standard kernel isn't able to is unneeded and inflamitory. > The question was not about RTLInux but so called standard Linux kernel. I know that. ...and I also know that standard linux supports SCHED_RR and SCHED_FIFO. I use them daily for soft realtime tasks and have tested their behavior. They are there, they have been for a long time and they work. For a true standard kernel on an IA32 system, a typcal embedded system (no one flipping consoles) can provide worst case latencies around 100-200ms with typical latencies under 10-20ms. Simple changes don't yet make much different to the worst case (I still see 60ms) but improve the typical to more like 2ms. I can actually run a 1ms period where (sorry didn't do real stats) the vast majority (almost certainly better than 95%) of latencies where around 100us or better. What I have described is (for most people) a soft realtime capable system. In other words, it is suitable for tasks that degrade rather than fail catistrophically when deadlines aren't met. It is suitable for these tasks down to the sub-10ms range. If you need hard realtime then you had better not plan on better than 100-200ms as it can get that bad. Standard linux DOES support SCHED_FIFO and priorities. If you create a SCHED_FIFO thread that doesn't ever sleep your user level system will effectively lock. This is what prioritized scheduling is supposed to do. > -ishwar Ty -- Tyson D Sawyer iRobot Corporation Senior Systems Engineer Military Systems Division [EMAIL PROTECTED] Robots for the Real World 603-532-6900 ext 206 http://www.irobot.com -- [rtl] --- To unsubscribe: echo "unsubscribe rtl" | mail [EMAIL PROTECTED] OR echo "unsubscribe rtl <Your_email>" | mail [EMAIL PROTECTED] -- For more information on Real-Time Linux see: http://www.rtlinux.org/
