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? Of course with this patchset this might not be possible, but I have elaborated my point below.
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. I observed this when looking at tuned. Tuned sets the cpu_dma_latency depending on what it reads from /proc/loadavg. This would mean for a small number of short running tasks also this metric could reflect a number which makes it look like the system is loaded reasonably. It then disables deep idle states by setting a high pm_qos latency requirement for system. This is bad because it disables power savings even on a lightly loaded system. This is just an example of how users of /proc/loadavg could make the wrong decisions based on an inaccurate measure of system load. Do you think we must take a look again at the avenrun[] array and update it to reflect the right cpu load average? Regards Preeti U Murthy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
