Issue #15438 has been updated by sylvain.joyeux (Sylvain Joyeux).


`RUBY_THREAD_PRIORITY_MIN` is changed to give the developer the choice to make some threads really low priority, at the cost of switching overhead. Unless I'm mistaken, the semantic of 'priority' right now is very platform-specific anyways (depends on the underlying thread scheduling implementation), so I don't see a major drive in making the min and max value uniform across all Ruby implementations.

If this indeed is a problem, I'll just switch it back to -3.

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Bug #15438: Threads can't switch faster than TIME_QUANTUM_(NSEC|USEC|MSEC)
https://bugs.ruby-lang.org/issues/15438#change-77088

* Author: sylvain.joyeux (Sylvain Joyeux)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: trunk
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN
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Thread#priority can be set to negative values, which when looking at the code is meant to reduce the time allocated to the thread. However, as far as I could understand in the codebase, the quantum of time is definitely hard-coded to 100ms (TIME_QUANTUM_...). This means that the "lower allocated time" would only work for threads that would often yield one way or the other (sleep, blocking calls, ...)

My projects would definitely benefit from a faster switching period. I was wondering how best to implement this ability ?

I thought of the following:

1. globally using an environment variable
2. globally using an API
3. trying to adapt dynamically, using the highest needed period
4. lowering the period when a priority lower than 0 is set, leaving it at the lower period.

Obviously (3) would seem to be the best, but I'm not sure I would be able to get it right in a decent amount of time. (4) seem to be a good trade-off between simplicity and performance (nothing changes if you never use priorities lower than 0, and if you were you basically get what you wanted).

What do you think ?

---Files--------------------------------
0001-dynamically-modify-the-timer-thread-period-to-accoun.patch (3.12 KB)
0001-2.6-fix-handling-of-negative-priorities.patch (8.43 KB)


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