On Thu, Sep 05, 2019 at 12:18:55PM +0100, Patrick Bellasi wrote: > Right, we have this dualism to deal with and current mainline behaviour > is somehow in the middle. > > BTW, the FB requirement is the same we have in Android. > We want some CFS tasks to have very small latency and a low chance > to be preempted by the wake-up of less-important "background" tasks. > > I'm not totally against the usage of a signed range, but I'm thinking > that since we are introducing a new (non POSIX) concept we can get the > chance to make it more human friendly.
I'm arguing that signed _is_ more human friendly ;-) > Give the two extremes above, would not be much simpler and intuitive to > have 0 implementing the FB/Android (no latency) case and 1024 the > (max latency) Oracle case? See, I find the signed thing more natural, negative is a bias away from latency sensitive, positive is a bias towards latency sensitive. Also; 0 is a good default value ;-) > Moreover, we will never match completely the nice semantic, give that > a 1 nice unit has a proper math meaning, isn't something like 10% CPU > usage change for each step? Only because we were nice when implementing it. Posix leaves it unspecified and we could change it at any time. The only real semantics is a relative 'weight' (opengroup uses the term 'favourable'). > Could changing the name to "latency-tolerance" break the tie by marking > its difference wrt prior/nice levels? AFAIR, that was also the original > proposal [1] by PaulT during the OSPM discussion. latency torrerance could still be a signed entity, positive would signify we're more tolerant of latency (ie. less sensitive) while negative would be less tolerant (ie. more sensitive). > For latency-nice instead we will likely base our biasing strategies on > some predefined (maybe system-wide configurable) const thresholds. I'm not quite sure; yes, for some of these things, like the idle search on wakeup, certainly. But say for wakeup-preemption, we could definitely make it a task relative attribute.
