On Wed, 2007-04-25 at 22:13 +0200, Willy Tarreau wrote: > On Wed, Apr 25, 2007 at 04:58:40AM -0700, William Lee Irwin III wrote: > > > Adjustments to the lag computation for for arrivals and departures > > during execution are among the missing pieces. Some algorithmic devices > > are also needed to account for the varying growth rates of lags of tasks > > waiting to run, which arise from differing priorities/weights. > > that was the principle of my proposal of sorting tasks by expected completion > time and using +/- credit to compensate for too large/too short slice used. > > Willy
Yeah, it's a good algorithm. It's a variant of earliest deadline first (EDF). There are also similar ones in the literature such as earliest eligible virtual deadline first (EEVDF) and biased virtual finishing time (BVFT). Based on wli's explanation, I think Ingo's approach would also fall into this category. With careful design, all such algorithms that order tasks based on some notion of time can achieve good fairness. There are some subtle differences. Some algorithms of this type can achieve a constant lag bound, but some only have a constant positive lag bound, but O(N) negative lag bound, meaning some tasks could receive much more CPU time than it would under ideal fairness when the number of tasks is high. On the other hand, the log(N) complexity of this type of algorithms has been a concern in the research community. This motivated O(1) round-robin based algorithms such as deficit round-robin (DRR) and smoothed round-robin (SRR) in networking, and virtual-time round-robin (VTRR), group ratio round-robin (GP3) and grouped distributed queues (GDQ) in OS scheduling, as well as the distributed weighted round-robin (DWRR) one I posted earlier. tong - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
