Messages in this thread | | | Subject | Re: [PATCH RFC 1/3] sched: introduce distinct per-cpu load average | From | Peter Zijlstra <> | Date | Thu, 04 Oct 2012 14:12:08 +0200 |
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On Thu, 2012-10-04 at 11:43 +0200, Andrea Righi wrote: > > Right, the update must be atomic to have a coherent nr_uninterruptible > value. And AFAICS the only way to account a coherent > nr_uninterruptible > value per-cpu is to go with atomic ops... mmh... I'll think more on > this.
You could stick it in the cpu controller instead of cpuset, add a per-cpu nr_uninterruptible counter to struct task_group and update it from the enqueue/dequeue paths. Those already are per-cgroup (through cfs_rq, which has a tg pointer).
That would also give you better semantics since it would really be the load of the tasks of the cgroup, not whatever happened to run on a particular cpu regardless of groups. Then again, it might be 'fun' to get the hierarchical semantics right :-)
OTOH it would also make calculating the load-avg O(nr_cgroups) and since we do this from the tick and people are known to create a shitload (on the order of 1e3 and upwards) of those this might not actually be a very good idea.
Also, your patch 2 relies on the load avg function to be additive yet your completely fail to mention this and state whether this is so or not.
Furthermore, please look at PER_CPU() and friends as alternatives to [NR_CPUS] arrays.
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