Messages in this thread | | | Date | Sat, 25 May 2002 17:39:00 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: patent on O_ATOMICLOOKUP [Re: [PATCH] loopable tmpfs (2.4.17)] |
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On Sat, 25 May 2002, Linus Torvalds wrote: > > Can we make the whole kernel truly hard-RT? Sure, possible in theory. In > practice? No way, José. It's just not mainline enough.
Side note: we could, of course, mark some spinlocks (and thus some code-paths) as being RT-safe, and then make sure that those spinlocks - when they disable interrupts - actually disable the _hw_ interrupts even with the RT patches.
That would make those sequences usable even from within a RT subset, but would obviously mean that those spinlocks have to be checked for latency issues - because any user (also non-RT ones) would obviously be truly uninterruptible within these spinlocks.
Every single RT person out there is already painfully aware of (and used to) having to limit the set of functions he can use while RT, so this is something you guys tend to be pretty familiar with..
So the "hard-RT" thing doesn't need to be a complete on/off thing.
This kind of "limited kernel functionality" tends to help only RT kernel modules, though. Full system calls (except the trivial ones like "getpid()", of course) simply tend to have to require too much "real" infrastructure that they can't use the RT subset.
Also, some people will he happy to know that soft-RT ends up getting continually improved, and many people might be able to find that just the regular preemptible kernel gives good enough latency at least if you can limit the workload on the machine (which, on embedded devices tends to be somethin gyou take for granted anyway).
That may not make the hard RT people happier, but at least it might shrink the number of the die-hard hard RT'rs.
"If you can't beat them, try to make them extinct" ;)
Linus
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