.@paulmckrcu Would it be possible to do "norcu" as "synchronize on every return to userspace and every cpu_idle entry"?
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Replying to @RichFelker
If you don't mind long loops in the kernel stalling RCU and OOMing your system, yes... But what are you trying to achieve?
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Replying to @paulmckrcu
Unpredictable and possibly unbounded memory usage and performance characteristics and seemingly impossible-to-verify logic.
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Replying to @RichFelker @paulmckrcu
Or rather, trying to avoid those things. So frustrating debugging this stuff when simple rwlocks & no alloc would've sufficed.
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Replying to @RichFelker @paulmckrcu
What I'm trying to say is it'd be nice to have an option that doesn't depend on the scheduler to collect, does it sync. instead.
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Replying to @RichFelker
: But the real problem was not the scheduler, but rather timers, correct? Or am I behind the times in your troubleshooting?
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Replying to @paulmckrcu
I don't know, This thread is inspired by but in some sense orthogonal to current stall problem.
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Replying to @RichFelker @paulmckrcu
Mainly frustration that embed/dt/server systems need huge complex feedback system "designed for...hundreds or thousands of CPUs"
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Replying to @RichFelker @paulmckrcu
...when they would perform at least as well, and much more predictably, with simple rwlocks or similar.
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Replying to @RichFelker
You could write a SMP RCU for small systems. However, it would still have CPU stall warnings. Not clear it would help you.
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It seems like, in principle, TINY_RCU+locks should work for SMP.
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Replying to @RichFelker
In practice, as discussed earlier, use of lock for RCU in Linux kernel gets you deadlock, etc.
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