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In those systems, the Linux kernel tends to be compartmentalised, basically being run as a task under the control of the real RTOS while the safety critical & h

In those systems, the Linux kernel tends to be compartmentalised, basically being run as a task under the control of the real RTOS while the safety critical & hard real-time portions are run in a proper RTOS. The other situation is that the actual control is deferred to a proper RTOS/micro combination which can do the correct thing when Linux goes off the rails. The Linux kernel is not a hard-real-time system, it doesn't have complete test coverage and its inclusion in highly-safety-critical systems is as a lower-safety-level subsystem. You will not find a Linux task controlling (for example) a GPIO enabling an X-Ray beam in human rated medical devices. BTW: I can promise you that there are many untested goto's in the Linux Kernel...

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fit2rule 11y ago
"proper" RTOS. What part of Linux precludes it from being a proper RT OS in the hands of industrial developers whose purpose it is to certify it as such? >BTW: I can promise you that there are many untested goto's in the Linux Kernel... Not in a development environment looking for SIL-4 certification, there isn't. Perhaps in the public sphere you may feel that is an adequate position, but in industrial computing a significant part of the value is in the testing and real certification of the Linux kernel for certain ratings. >The Linux kernel is not a hard-real-time system, it doesn't have complete test coverage and its inclusion in highly-safety-critical systems is as a lower-safety-level subsystem I assure you, I have found none of these statements to be truly true.
- TickleSteve 11y ago
  The linux kernel is tuned for throughput, not latency and certainly not bounded-latency. My background is industrial/defense/medical s/w on hard real time systems. e.g. I've worked on train braking systems, high throughput radar systems, medical devices, lots hard real-time control stuff.... I personally have never seen any evidence of anything greater than SIL-2 certified Linux (https://www.osadl.org/SIL2LinuxMP.sil2-linux-project.0.html https://www.osadl.org/SIL2LinuxMP.sil2-linux-project.0.html) and that is only in very narrowly defined context. Like I said earlier, any higher certification, Linux would be run as a comparmentalised, lower-level subsystem. The real control would not be via a Linux controlled task. Until you can point me to the test-suite for a Linux kernel& driver set that gives me 100% code-coverage, then Linux will never get past this point. Dont get me wrong, I like Linux and it has a valuable place in embedded systems.... but hard-real-time control and safety-related systems is not it. As a final word on the subject, dont take my word for it: http://www.hse.gov.uk/research/rrhtm/rr011.htm http://www.hse.gov.uk/research/rrhtm/rr011.htm "it is not likely to be either suitable or certifiable for SIL 4 applications" "It is unlikely that Linux would be useful for SIL 4 applications and it would not be reasonably practicable to provide evidence that it meets a SIL 4 integrity requirement. " ...And in (https://www.osadl.org/fileadmin/dam/presentations/61508/61508_paper.pdf https://www.osadl.org/fileadmin/dam/presentations/61508/6150...) "One of the main conclusion: Linux is not suitable for SIL4."
  - fit2rule 11y ago
    >Until you can point me to the test-suite for a Linux kernel& driver set that gives me 100% code-coverage, then Linux will never get past this point. Of course, this is proprietary to the whims of the companys' deploying SIL-4 Linux: THALES, et al. http://ti.tuwien.ac.at/ecs/teaching/courses/hwswcode_vu_WS_2011/hwsw-codesign-student-presentations/gv1-thales http://ti.tuwien.ac.at/ecs/teaching/courses/hwswcode_vu_WS_2... http://ercim-news.ercim.eu/en75/special/tas-control-platform-a-platform-for-safety-critical-railway-applications http://ercim-news.ercim.eu/en75/special/tas-control-platform... http://www.ibm.com/developerworks/library/l-real-time-linux/ http://www.ibm.com/developerworks/library/l-real-time-linux/ (BTW, HSE isn't exactly an industrial authority on much ..)
    - TickleSteve 11y ago
      > Of course, this is proprietary to the whims of the companys' deploying SIL-4 Linux: THALES, et al. I've worked with Thales companies many times in the past. Never seen any evidence of Sil4 Linux. And no, this is absolutely not at the whim of the companies deploying it. >http://ti.tuwien.ac.at/ecs/teaching/courses/hwswcode_vu_WS_2.. http://ti.tuwien.ac.at/ecs/teaching/courses/hwswcode_vu_WS_2.... No mention of Linux. > http://ercim-news.ercim.eu/en75/special/tas-control-platform.. http://ercim-news.ercim.eu/en75/special/tas-control-platform.... 1 mention of Linux... no mention of the role it plays. >http://www.ibm.com/developerworks/library/l-real-time-linux/ http://www.ibm.com/developerworks/library/l-real-time-linux/ Verifies my point. Only the kernel-in-kernel/hypervisor systems get hard-real-time performance. This is necessary for safety-critical work. > (BTW, HSE isn't exactly an industrial authority on much ..) HSE == Health & Safety Executive... they are very much involved in this.... they're the government authority related to this type of stuff. They license software for use in Nuclear Reactors and the like (along with other agencies). My points absolutely still stand.
      - fit2rule 11y ago
        Hint: I was on the team that released TAS PLF 2.x, and it is definitely SIL4, definitely hard real-time, and definitely a well-maintained Linux project which many other divisions (i.e. Space) also come to use as a reference platform. I suggest you simply missed it: its running an awful lot of rail transportation systems around the world, though...
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fit2rule 11y ago

"proper" RTOS. What part of Linux precludes it from being a proper RT OS in the hands of industrial developers whose purpose it is to certify it as such? >BTW: I can promise you that there are many untested goto's in the Linux Kernel... Not in a development environment looking for SIL-4 certification, there isn't. Perhaps in the public sphere you may feel that is an adequate position, but in industrial computing a significant part of the value is in the testing and real certification of the Linux kernel for certain ratings. >The Linux kernel is not a hard-real-time system, it doesn't have complete test coverage and its inclusion in highly-safety-critical systems is as a lower-safety-level subsystem I assure you, I have found none of these statements to be truly true.

TickleSteve 11y ago
The linux kernel is tuned for throughput, not latency and certainly not bounded-latency. My background is industrial/defense/medical s/w on hard real time systems. e.g. I've worked on train braking systems, high throughput radar systems, medical devices, lots hard real-time control stuff.... I personally have never seen any evidence of anything greater than SIL-2 certified Linux (https://www.osadl.org/SIL2LinuxMP.sil2-linux-project.0.html https://www.osadl.org/SIL2LinuxMP.sil2-linux-project.0.html) and that is only in very narrowly defined context. Like I said earlier, any higher certification, Linux would be run as a comparmentalised, lower-level subsystem. The real control would not be via a Linux controlled task. Until you can point me to the test-suite for a Linux kernel& driver set that gives me 100% code-coverage, then Linux will never get past this point. Dont get me wrong, I like Linux and it has a valuable place in embedded systems.... but hard-real-time control and safety-related systems is not it. As a final word on the subject, dont take my word for it: http://www.hse.gov.uk/research/rrhtm/rr011.htm http://www.hse.gov.uk/research/rrhtm/rr011.htm "it is not likely to be either suitable or certifiable for SIL 4 applications" "It is unlikely that Linux would be useful for SIL 4 applications and it would not be reasonably practicable to provide evidence that it meets a SIL 4 integrity requirement. " ...And in (https://www.osadl.org/fileadmin/dam/presentations/61508/61508_paper.pdf https://www.osadl.org/fileadmin/dam/presentations/61508/6150...) "One of the main conclusion: Linux is not suitable for SIL4."
- fit2rule 11y ago
  >Until you can point me to the test-suite for a Linux kernel& driver set that gives me 100% code-coverage, then Linux will never get past this point. Of course, this is proprietary to the whims of the companys' deploying SIL-4 Linux: THALES, et al. http://ti.tuwien.ac.at/ecs/teaching/courses/hwswcode_vu_WS_2011/hwsw-codesign-student-presentations/gv1-thales http://ti.tuwien.ac.at/ecs/teaching/courses/hwswcode_vu_WS_2... http://ercim-news.ercim.eu/en75/special/tas-control-platform-a-platform-for-safety-critical-railway-applications http://ercim-news.ercim.eu/en75/special/tas-control-platform... http://www.ibm.com/developerworks/library/l-real-time-linux/ http://www.ibm.com/developerworks/library/l-real-time-linux/ (BTW, HSE isn't exactly an industrial authority on much ..)
  - TickleSteve 11y ago
    > Of course, this is proprietary to the whims of the companys' deploying SIL-4 Linux: THALES, et al. I've worked with Thales companies many times in the past. Never seen any evidence of Sil4 Linux. And no, this is absolutely not at the whim of the companies deploying it. >http://ti.tuwien.ac.at/ecs/teaching/courses/hwswcode_vu_WS_2.. http://ti.tuwien.ac.at/ecs/teaching/courses/hwswcode_vu_WS_2.... No mention of Linux. > http://ercim-news.ercim.eu/en75/special/tas-control-platform.. http://ercim-news.ercim.eu/en75/special/tas-control-platform.... 1 mention of Linux... no mention of the role it plays. >http://www.ibm.com/developerworks/library/l-real-time-linux/ http://www.ibm.com/developerworks/library/l-real-time-linux/ Verifies my point. Only the kernel-in-kernel/hypervisor systems get hard-real-time performance. This is necessary for safety-critical work. > (BTW, HSE isn't exactly an industrial authority on much ..) HSE == Health & Safety Executive... they are very much involved in this.... they're the government authority related to this type of stuff. They license software for use in Nuclear Reactors and the like (along with other agencies). My points absolutely still stand.
    - fit2rule 11y ago
      Hint: I was on the team that released TAS PLF 2.x, and it is definitely SIL4, definitely hard real-time, and definitely a well-maintained Linux project which many other divisions (i.e. Space) also come to use as a reference platform. I suggest you simply missed it: its running an awful lot of rail transportation systems around the world, though...

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