On 7 January 2014 14:22, Peter Zijlstra <[email protected]> wrote: > On Tue, Jan 07, 2014 at 09:32:04AM +0100, Vincent Guittot wrote: >> On 6 January 2014 17:31, Peter Zijlstra <[email protected]> wrote: >> > On Mon, Jan 06, 2014 at 02:41:31PM +0100, Vincent Guittot wrote: >> >> IMHO, these settings will disappear sooner or later, as an example the >> >> idle/busy _idx are going to be removed by Alex's patch. >> > >> > Well I'm still entirely unconvinced by them.. >> > >> > removing the cpu_load array makes sense, but I'm starting to doubt the >> > removal of the _idx things.. I think we want to retain them in some >> > form, it simply makes sense to look at longer term averages when looking >> > at larger CPU groups. >> > >> > So maybe we can express the things in log_2(group-span) or so, but we >> > need a working replacement for the cpu_load array. Ideally some >> > expression involving the blocked load. >> >> Using the blocked load can surely give benefit in the load balance >> because it gives a view of potential load on a core but it still decay >> with the same speed than runnable load average so it doesn't solve the >> issue for longer term average. One way is to have a runnable average >> load with longer time window > > Ah, another way of looking at it is that the avg without blocked > component is a 'now' picture. It is the load we are concerned with right > now. > > The more blocked we add the further out we look; with the obvious limit > of the entire averaging period. > > So the avg that is runnable is right now, t_0; the avg that is runnable + > blocked is t_0 + p, where p is the avg period over which we expect the > blocked contribution to appear. > > So something like: > > avg = runnable + p(i) * blocked; where p(i) \e [0,1] > > could maybe be used to replace the cpu_load array and still represent > the concept of looking at a bigger picture for larger sets. Leaving open > the details of the map p.
That needs to be studied more deeply but that could be a way to have a larger picture Another point is that we are using runnable and blocked load average which are the sum of load_avg_contrib of tasks but we are not using the runnable_avg_sum of the cpus which is not the now picture but a average of the past running time (without taking into account task weight) Vincent -- 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/
