On Thu, Sep 05, 2019 at 12:40:30 +0100, Peter Zijlstra wrote...
> 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 ;-) ... but you are not human. :) >> 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 ;-) Yes, that's appealing indeed. >> 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'). Good to know, I was considering it a POXIS requirement. >> 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). Right. >> 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. -- #include <best/regards.h> Patrick Bellasi
