latency-test, latency-histogram: warn when rtapi_app lacks RT privileges#4107
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latency-test, latency-histogram: warn when rtapi_app lacks RT privileges#4107grandixximo wants to merge 2 commits into
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Without 'sudo make setuid' (or 'sudo make setcap') rtapi_app runs unprivileged: no SCHED_FIFO, no locked memory, so latency readings are wildly inflated and easy to mistake for a code regression. Warn, for a non-root user, when rtapi_app is neither setuid root nor carries the cap_sys_nice capability. Closes LinuxCNC#4044
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These tests are moot when you run on a non-RT kernel (like I do in dev). I'm not sure the noise is really necessary in that case. |
Only warn under PREEMPT_RT or RTAI; on a non-RT kernel the privileges do not matter, so the check would be noise.
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silenced on non-rt |
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Great. Every little bit helps. Reduces user frustration and more importantly less developer time wasted on spurious issues. |
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What
Both latency tools now warn, for a non-root user, when
rtapi_appis neither setuid root nor carrying thecap_sys_nicefile capability. In that state the realtime threads cannot get SCHED_FIFO scheduling or locked memory, so the reported latency is wildly inflated and unrepresentative.Why
In #4044 a run-in-place build was used without
sudo make setuid.rtapi_appran unprivileged, the latency numbers blew up, and this was initially mistaken for a code regression. It was not; the setuid/setcap step had simply been skipped. A plain warning would have saved the back-and-forth. @rodw-au suggested ageteuid()/setuid check in the issue thread.How
A small check runs before the test starts:
rtapi_app; if not found, stay silent.sudo make setuid): silent.cap_sys_nicefile capability present (sudo make setcap): silent.A pure euid check was deliberately avoided: a normal deb install runs the scripts as an unprivileged user yet works fine via setuid-root
rtapi_app, so euid alone would false-warn on every correct install. The real signal is the privilege state ofrtapi_appitself.latency-test(bash) prints to stderr;latency-histogram(tcl) prints to stderr and, in GUI mode, also shows atk_messageBox.Closes #4044