Messages in this thread | | | From | Con Kolivas <> | Subject | Re: [RFC 0/5] sched: Add CPU rate caps | Date | Sat, 27 May 2006 11:42:43 +1000 |
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On Saturday 27 May 2006 11:28, Peter Williams wrote: > Con Kolivas wrote: > > On Friday 26 May 2006 14:20, Peter Williams wrote: > >> Although the rlimit mechanism already has a CPU usage limit (RLIMIT_CPU) > >> it is a total usage limit and therefore (to my mind) not very useful. > >> These patches provide an alternative whereby the (recent) average CPU > >> usage rate of a task can be limited to a (per task) specified proportion > >> of a single CPU's capacity. The limits are specified in parts per > >> thousand and come in two varieties -- hard and soft. > > > > Why 1000? > > Probably a hang over from a version where the units were proportion of a > whole machine. Percentage doesn't work very well if there are more than > 1 CPU in that case (especially if there are more than 100 CPUs :-)). > But it's also useful to have the extra range if your trying to cap > processes (or users) from outside the scheduler using these primitives. > > > I doubt that degree of accuracy is possible in cpu accounting and > > accuracy or even required. To me it would seem to make more sense to just > > be a percentage. > > It's not meant to imply accuracy :-). The main issue is avoiding > overflow when doing the multiplications during the comparisons.
Well you could always expose a smaller more meaningful value than what is stored internally. However you've already implied that there are requirements in userspace for more granularity in the proportioning than percentage can give.
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