[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH RFC v2 5/7] libxl/vNUMA: VM config parsing functions
On Mon, Oct 14, 2013 at 9:26 AM, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx> wrote: > Dario Faggioli writes ("Re: [Xen-devel] [PATCH RFC v2 5/7] libxl/vNUMA: VM > config parsing functions"): >> On ven, 2013-10-11 at 12:18 +0100, Ian Jackson wrote: >> > Aren't there some constraints that need to be imposed ? For example, >> > distance[X,Y]==distance[Y,X] ? What about the triangle inequality >> > (distance[A,B] + distance[B,C] >= distance[A,C]) ? >> > >> I think Linux does some sanity checking of the distance table (and I >> think it disables NUMA if finding out something weird, Elena?). However, >> this (what Linux expects/checks for) shouldn't really be the only >> criterion, since although Linux is the only current implementation, >> there is no reason why this can't be implemented by other OSes. > > I wasn't really asking about Linux. I was talking about NUMA systems > in general. The thing which prompted me to ask is simply that I want > to be sure that the set of checks we perform has been deliberately > chosen, to reflect the actual potential nature of NUMA systems. > > You have chosen to call this parameter "distance". In mathematics, a > distance would normally have both the symmetry and triangle > inequality, as well as a number of other properties: > https://en.wikipedia.org/wiki/Metric_space#Definition > > What subset of those properties are true of NUMA distances ? (I > assume that these NUMA distances are estimates to be used by > heuristics, rather than actual measurements of a specific underlying > property.) Ian, I think the distance as you say its not a geometrical distance. In that case, I am not even sure if that triangle inequality should hold. I may be wrong. And NUMA distance is something that vendor defines. > >> > If we do need this I think the nested lists are probably a better >> > syntax for specifying the whole array. >> >> Agreed. I actually wanted to say the same. Would something like this be >> ok? >> >> distances = [ [10, 20], [20, 10] ] > > Right. I don't think there is anything preventing us implementing > this in the parser, although the existing code probably doesn't > support it. I can help with the parser. Sure, that would be great! Id like to work on this too, but the timing may not permit it untill end of October. > > ... >> distances = [ [10, 20, 30, 40], >> [10, 20, 30], >> [10, 20], >> [10] ] >> >> (I.e., "distances = [ [10, 20, 30, 40], [10, 20, 30], [10, 20], [10] ]) > > I'd suggest that we should expect the user to specify the lower left > half, rather than the upper right. That avoids the counterintuitive > offset of the indices in subsequent rows. > > (Also I observe that your example violates distance[A,B] == 0.) > > Ian. -- Elena _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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