* menage@xxxxxxxxxx <menage@xxxxxxxxxx> [2009-06-05 01:53:15]: > 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 ...) The important scenario I have is adding and removing groups. Consider 10 cgroups with shares of 10 each, what if 5 new are created with the same shares? We now start getting 100/15, even though we did not change our shares. -- Balbir -- 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
