On Fri, Jun 05, 2009 at 04:02:11PM +0300, Avi Kivity wrote: > Paul Menage wrote: >> 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 ...) >> > > How many shares does a cgroup with a 0% guarantee get? > Shares cannot be used to provide guarantees. All they decide is what propotion groups can get CPU time. (yes, shares is a bad name, weight shows the intent better). thanks, -- regards, Dhaval -- 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
