On 05/06/2014 05:09 PM, Peter Zijlstra wrote: > On Tue, May 06, 2014 at 03:24:13PM +0530, Preeti Murthy wrote: >> Hi Morten, Peter, Alex, >> >> In a similar context, I noticed that /proc/loadavg makes use of >> avenrun[] array which keeps track of the history of the global >> load average. This however makes use of the sum of >> nr_running + nr_uninterruptible per cpu. Why are we not >> using the cpu_load[] array here which also keeps track >> of the history of per-cpu load and then return a sum of it? > > Entirely different kind of 'load'. Note that you cannot use > ->nr_uninterruptible per-cpu, also note that sched/proc.c doesn't.
True, I worded it wrong above. It uses the per_cpu nr_running and a global nr_uninterruptible. > >> Using nr_running to show the global load average would >> be misleading when entire load balancing is being done on the >> basis of the history of cfs_rq->runnable_load_avg/cpu_load[] >> right? IOW, to the best of my understanding we do not use >> nr_running anywhere to directly determine cpu load in the kernel. >> >> My idea was that the global/per_cpu load that we reflect via >> proc/sys interfaces must be consistent. I haven't really >> looked at what /proc/schedstat, /proc/stat, top are all reading >> from. But /proc/loadavg is reading out global nr_running + >> waiting tasks when this will not give us the accurate picture >> of the system load especially when there are many short running >> tasks. > > Nobody said /proc/loadavg is a sane number, but its what it is and since > its a global number its entirely unsuited for balancing -- not to > mention all other reasons its crap. I agree its not meant for balancing. My point was that since its inaccurate why don't we correct it. But if your argument is that we can live with /proc/loadavg showing a reasonable view of system load then it shouldn't be a problem. Regards Preeti U Murthy > -- 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/
