Hi, On 03/26/2013 05:56 PM, Peter Zijlstra wrote: > On Fri, 2013-03-22 at 13:25 +0100, Vincent Guittot wrote: >> +static bool is_buddy_busy(int cpu) >> +{ >> + struct rq *rq = cpu_rq(cpu); >> + >> + /* >> + * A busy buddy is a CPU with a high load or a small load with >> a lot of >> + * running tasks. >> + */ >> + return (rq->avg.runnable_avg_sum > >> + (rq->avg.runnable_avg_period / (rq->nr_running >> + 2))); >> +} > > Why does the comment talk about load but we don't see it in the > equation. Also, why does nr_running matter at all? I thought we'd > simply bother with utilization, if fully utilized we're done etc.. >
Peter, lets say the run-queue has 50% utilization and is running 2 tasks. And we wish to find out if it is busy. We would compare this metric with the cpu power, which lets say is 100. rq->util * 100 < cpu_of(rq)->power. In the above scenario would we declare the cpu _not_busy? Or would we do the following: (rq->util * 100) * #nr_running < cpu_of(rq)->power and conclude that it is just enough _busy_ to not take on more processes? @Vincent: Yes the comment above needs to be fixed. A busy buddy is a CPU with *high rq utilization*, as far as the equation goes. 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/