Re: [kvm-devel] [PATCH 0/2][KVM] guest time accounting

[Avi Kivity <avi@qumranet.com>]

Laurent Vivier wrote:
> The aim of these two patches is to measure the CPU time used by a virtual
> machine. All comments are welcome... I'm not sure it's the good way to do that.
>
> [PATCH 1/2] introduce a new field, "guest", in cpustat to store the time used by
> the CPU to run virtual CPU. Modify /proc/stat to display this new field.
>
> [PATCH 2/2] modify account_system_time() to add cputime to cpustat->guest if we
> are running a VCPU. We add this cputime to  cpustat->user instead of
> cpustat->system because this part of KVM code is in fact user code although it
> is executed in the kernel. We duplicate VCPU time between guest and user to
> allow an unmodified "top(1)" to display correct value. A modified "top(1)" is
> able to display good cpu user time and cpu guest time by subtracting cpu guest
> time from cpu user time.
>   

[copying Ingo and Rusty]

The patches look good.  A couple of comments:

- perhaps the new fields should be guarded by a #ifdef CONFIG_HYPERVISOR 
(selected by CONFIG_KVM)?  that way the (minor) additional overhead is 
only incurred if it can possibly be used.  I imagine that our canine 
cousin will want to use this as well.

- I think that there is per-task accounting of user time and system 
time; that should be extended as well.



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