On Mon, Aug 24, 2015 at 2:02 PM, Tejun Heo <tj@xxxxxxxxxx> wrote: > Hello, > > On Mon, Aug 24, 2015 at 01:54:08PM -0700, Paul Turner wrote: >> > That alone doesn't require hierarchical resource distribution tho. >> > Setting nice levels reasonably is likely to alleviate most of the >> > problem. >> >> Nice is not sufficient here. There could be arbitrarily many threads >> within the hypervisor that are not actually hosting guest CPU threads. >> The only way to have this competition occur at a reasonably fixed >> ratio is a sub-hierarchy. > > I get that having hierarchy of threads would be nicer but am having a > bit of difficulty seeing why adjusting priorities of threads wouldn't > be sufficient. It's not like threads of the same process competing > with each other is a new problem. People have been dealing with it > for ages. Hierarchical management can be a nice plus but we want the > problem and proposed solution to be justifiable. Consider what happens with load asymmetry: Suppose that we have 10 vcpu threads and 100 support threads. Suppose that we want the support threads to receive up to 10% of the time available to the VM as a whole on that machine. If I have one particular support thread that is busy, I want it to receive that entire 10% (maybe a guest is pounding on scsi for example, or in the thread-pool case, I've passed a single expensive computation). Conversely, suppose the guest is doing lots of different things and several support threads are active, I want the time to be shared between them. There is no way to implement this with nice. Either a single thread can consume 10%, and the group can dominate, or the group cannot dominate and the single thread can be starved. > > Thanks. > > -- > tejun -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
