On Fri, Jun 19, 2015 at 03:57:24PM +0800, Boqun Feng wrote: > > > > This rewrite patch does not NEED to aggregate entity's load to cfs_rq, > > but rather directly update the cfs_rq's load (both runnable and blocked), > > so there is NO NEED to iterate all of the cfs_rqs. > > Actually, I'm not sure whether we NEED to aggregate or NOT. > > > > > So simply updating the top cfs_rq is already equivalent to the stock. > >
Ok. By aggregate, the rewrite patch does not need it, because the cfs_rq's load is calculated at once with all its runnable and blocked tasks counted, assuming the all children's weights are up-to-date, of course. Please refer to the changelog to get an idea. > > The stock does have a bottom up update, so simply updating the top > cfs_rq is not equivalent to it. Simply updateing the top cfs_rq is > equivalent to the rewrite patch, because the rewrite patch lacks of the > aggregation. It is not the rewrite patch "lacks" aggregation, it is needless. The stock has to do a bottom-up update and aggregate, because 1) it updates the load at an entity granularity, 2) the blocked load is separate. > > It is better if we iterate the cfs_rq to update the actually weight > > (update_cfs_share), because the weight may have already changed, which > > would in turn change the load. But update_cfs_share is not cheap. > > > > Right? > > You get me right for most part ;-) > > My points are: > > 1. We *may not* need to aggregate entity's load to cfs_rq in > update_blocked_averages(), simply updating the top cfs_rq may be just > fine, but I'm not sure, so scheduler experts' insights are needed here. Then I don't need to say anything about this. > 2. Whether we need to aggregate or not, the update_blocked_averages() in > the rewrite patch could be improved. If we need to aggregate, we have to > add something like update_cfs_shares(). If we don't need, we can just > replace the loop with one update_cfs_rq_load_avg() on root cfs_rq. If update_cfs_shares() is done here, it is good, but probably not necessary though. However, we do need to update_tg_load_avg() here, because if cfs_rq's load change, the parent tg's load_avg should change too. I will upload a next version soon. In addition, an update to the stress + dbench test case: I have a Core i7, not a Xeon Nehalem, and I have a patch that may not impact the result. Then, the dbench runs at very low CPU utilization ~1%. Boqun said this may result from cgroup control, the dbench I/O is low. Anyway, I can't reproduce the results, the CPU0's util is 92+%, and other CPUs have ~100% util. Thanks, Yuyang -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/
