[PATCH] io-controller: implement per group request allocation limitation
guijianfeng at cn.fujitsu.com
Mon Aug 3 23:38:35 PDT 2009
Munehiro Ikeda wrote:
> Consideration and Conclusion
> From result(1), it is observed that it takes 1000~1200[ms] to rise P2
> bandwidth. In result(2), where both of g1 and g2 have
> nr_group_requests=100, the delay gets longer as 1800~2000[ms]. In
> addition to it, the average bandwidth becomes ~5% lower than result(1).
> This is supposed that P2 couldn't allocate enough requests.
> Then, result(3) shows that bandwidth of P2 can rise quickly (~300[ms])
> if nr_group_requests can be set per-cgroup. Result(4) shows that the
> delay can be shortened by setting g2 as RT class, however, the delay is
> still longer than result(3).
> I think it is confirmed that "per-cgroup nr_requests limitation is
> useful in a certain situation". Beyond that, the discussion topic is
> the benefit pointed out above is eligible for the complication of the
> implementation. IMHO, I don't think the implementation of per-cgroup
> request limitation is too complicated to accept. On the other hand I
> guess it suddenly gets complicated if we try to implement further more,
> especially hierarchical support. It is also true that I have a feeling
> that implementation without per-device limitation and hierarchical
> support is like "unfinished work".
> So, my opinion so far is that, per-cgroup nr_requests limitation should
> be merged only if hierarchical support is concluded "unnecessary" for
> it. If merging it tempts hierarchical support, it shouldn't be.
> How about your opinion, all?
Thanks for the great job. It seems Per-cgroup requests allocation limits
has its value in some cases. IMHO, for the time being, we can just drop
the hierarchical support for "Per-cgroup requests allocation limits", and
see whether it can work well.
> My considerations or verification method might be wrong. Please correct
> them if any. And if you have any other idea of scenario to verify the
> effect of per-cgroup nr_requests limitation, please let me know. I'll
> try it.
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