Hello, On Mon, Dec 17, 2012 at 03:53:18PM -0500, Vivek Goyal wrote: > On Fri, Dec 14, 2012 at 02:41:20PM -0800, Tejun Heo wrote: > > Currently, cfqg charges are scaled directly according to cfqg->weight. > > Regardless of the number of active cfqgs or the amount of active > > weights, a given weight value always scales charge the same way. This > > works fine as long as all cfqgs are treated equally regardless of > > their positions in the hierarchy, which is what cfq currently > > implements. It can't work in hierarchical settings because the > > interpretation of a given weight value depends on where the weight is > > located in the hierarchy. > > I did not understand this. Why the current scheme will not work with > hierarchy? Because the meaning of a weight changes depending on where the weight exists in the hierarchy? > While we calculate the vdisktime, this is calculated with the help > of CFQ_DEFAULT_WEIGHT and cfqg->weight. So we scale used time slice > in proportion to CFQ_DEFAULT_WEIGTH/cfqg->weight. So higher the weight > lesser the charge and cfqg gets scheduled again faster and lower the > weight, higher the vdisktime and cfqg gets scheduled less frequently. > > As every cfqg does the same thing on service tree, they automatically > get fair share w.r.t their weight. > > And this mechanism should not be impacted by the hierarchy because we > have a separate service tree at separate level. This will not work > only if you come up with one compressed tree and then weights will > have to be adjusted. If we have a separate service tree in each group > then it should work just fine. Why would you create N service trees when you can almost trivially use one by calcualting the effective weight? You would have to be adjusting all trees above whenever something changes in a child. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
