Re: [Xen-devel] [PATCH 1/2] cpu steal time accounting

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 21 Feb 2006, at 19:32, Rik van Riel wrote:

> Basically steal time is the amount of time when:
> 1) we had a runnable task, but
> 2) it was not running, because our vcpu was scheduled
>    away by the hypervisor
>
> Thus, steal time measures how much a particular workload
> inside a virtual machine is impacted by contention on the
> cpu between different virtual machines.
>
> It also makes sure that time the vcpu itself was not running
> is not erroneously accounted to the currently running process,
> which matters when a user is trying to determine how much CPU
> time a particular task needs.
Is accounting user/system time an unnecessary extra? I guess we already 
do it by sampling at tick granularity anyway?
Should 'steal time' include blocked time when the guest had no work to 
execute?
Also, given the logic currently only triggers when the guest detects it 
'missed a tick', would it be good enough simply to account 
#missed_ticks as steal time. It would certainly be a lot simpler to 
implement, and you end up dividing everything down to tick granularity 
anyway. :-)
 -- Keir


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