On Wed, 2013-03-06 at 23:30 -0300, Marcelo Tosatti wrote: > On Wed, Mar 06, 2013 at 10:27:13AM -0600, Michael Wolf wrote: > > On Tue, 2013-03-05 at 22:41 -0300, Marcelo Tosatti wrote: > > > On Tue, Mar 05, 2013 at 02:22:08PM -0600, Michael Wolf wrote: > > > > Sorry for the delay in the response. I did not see the email > > > > right away. > > > > > > > > On Mon, 2013-02-18 at 22:11 -0300, Marcelo Tosatti wrote: > > > > > On Mon, Feb 18, 2013 at 05:43:47PM +0100, Frederic Weisbecker wrote: > > > > > > 2013/2/5 Michael Wolf <mjw@xxxxxxxxxxxxxxxxxx>: > > > > > > > In the case of where you have a system that is running in a > > > > > > > capped or overcommitted environment the user may see steal time > > > > > > > being reported in accounting tools such as top or vmstat. This can > > > > > > > cause confusion for the end user. > > > > > > > > > > > > Sorry, I'm no expert in this area. But I don't really understand what > > > > > > is confusing for the end user here. > > > > > > > > > > I suppose that what is wanted is to subtract stolen time due to 'known > > > > > reasons' from steal time reporting. 'Known reasons' being, for example, > > > > > hard caps. So a vcpu executing instructions with no halt, but limited to > > > > > 80% of available bandwidth, would not have 20% of stolen time reported. > > > > > > > > Yes exactly and the end user many times did not set up the guest and is > > > > not aware of the capping. The end user is only aware of the performance > > > > level that they were told they would get with the guest. > > > > > But yes, a description of the scenario that is being dealt with, with > > > > > details, is important. > > > > > > > > I will add more detail to the description next time I submit the > > > > patches. How about something like,"In a cloud environment the user of a > > > > kvm guest is not aware of the underlying hardware or how many other > > > > guests are running on it. The end user is only aware of a level of > > > > performance that they should see." or does that just muddy the picture > > > > more?? > > > > > > So the feature aims for is to report stolen time relative to hard > > > capping. That is: stolen time should be counted as time stolen from > > > the guest _beyond_ hard capping. Yes? > > Yes, that is the goal. > > > > > > Probably don't need to report new data to the guest for that. > > Not sure I understand what you are saying here. Do you mean that I don't > > need to report the expected steal from the guest? If I don't do that > > then I'm not reporting all of the time and changing /proc/stat in a > > bigger way than adding another catagory. Also I thought I would need to > > provide the consigned time and the steal time for debugging purposes. > > Maybe I'm missing your point..... > > OK so the usefulness of steal time comes from the ability to measure > CPU cycles that the guest is being deprived of, relative to some unit > (implicitly the CPU frequency presented to the VM). That way, it becomes > easier to properly allocate resources. > > From top man page: > st : time stolen from this vm by the hypervisor > > Not only its a problem for the lender, it is also confusing for the user > (who has to subtract from the reported value himself), the hardcapping > from reported steal time. > > > The problem with the algorithm in the patchset is the following > (practical example): > > - Hard capping set to 80% of available CPU. > - vcpu does not exceed its threshold, say workload with 40% > CPU utilization. > - Under this scenario it is possible for vcpu to be deprived > of cycles (because out of the 40% that workload uses, only 30% of > actual CPU time are being provided). > - The algorithm in this patchset will not report any stolen time > because it assumes 20% of stolen time reported via 'run_delay' > is fixed at all times (which is false), therefore any valid > stolen time below 20% will not be reported. > > Makes sense? > > Not sure what the concrete way to report stolen time relative to hard > capping is (probably easier inside the scheduler, where run_delay is > calculated). > > Reporting the hard capping to the guest is a good idea (which saves the > user from having to measure it themselves), but better done separately > via new field. didnt respond to this in the previous response. I'm not sure I'm following you here. I thought this is what I was doing by having a consigned (expected steal) field add to the /proc/stat output. Are you looking for something else or a better naming convention? > > > -- > 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 > -- 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
