On Wed, Jun 3, 2009 at 10:36 PM, Bharata B Rao<bharata@xxxxxxxxxxxxxxxxxx> wrote: > - Hard limits can be used to provide guarantees. > This claim (and the subsequent long thread it generated on how limits can provide guarantees) confused me a bit. Why do we need limits to provide guarantees when we can already provide guarantees via shares? Suppose 10 cgroups each want 10% of the machine's CPU. We can just give each cgroup an equal share, and they're guaranteed 10% if they try to use it; if they don't use it, other cgroups can get access to the idle cycles. Suppose cgroup A wants a guarantee of 50% and two others, B and C, want guarantees of 15% each; give A 50 shares and B and C 15 shares each. In this case, if they all run flat out they'll get 62%/19%/19%, which is within their SLA. That's not to say that hard limits can't be useful in their own right - e.g. for providing reproducible loadtesting conditions by controlling how much CPU a service can use during the load test. But I don't see why using them to implement guarantees is either necessary or desirable. (Unless I'm missing some crucial point ...) Paul -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
