[Kimchi-devel] RFC - Guest memory usage

[Suresh Babu Angadi]

On 10/27/2015 05:59 PM, Paulo Ricardo Paz Vital wrote:
> On Sun, 2014-12-07 at 23:16 -0200, Daniel Henrique Barboza wrote:
>> I was looking at the following item in the backlog:
>>
>> Guests	Stats: Display memory utilization (use virt-df or virt
>> -top or ...)
>> If I understood it right, the idea here is to show the -inner- memory
>> allocation of the guest. If you have a VM with 4Gb of RAM running an
>> Ubuntu, we want to know how much memory the Ubuntu OS and its
>> processes are using.
>>
>> I've done an investigation and I haven't found any tool to accomplish
>> this. "virt-top", "virsh dommemstat" and the libvirt API retrieves
>> the information of the memory usage of the guest relative to the
>> host. In the example mentioned before, supposing that the host has
>> 64Gb of RAM, all these tools would show that the VM is using 12% of
>> the host RAM. They do not dive in the VM and shows the actual mem
>> usage of the Ubuntu and its processes running there.
>>
>> Haven't found anything useful in other MLs and forums. The common
>> answer is 'run top in a terminal inside the VM', which of course does
>> not suit us. My question is: any thoughts about how we can implement
>> this feature? Because I am starting to think that, in the end, this
>> kind of info is strict to the guest OS and can't be polled from the
>> outside.
>>
> Looking again how to solve this, I could see that virt-manager and
> virsh have interfaces to provide the guest's memory usage. For example,
> using virsh you can get this kind of information:
>
> $ sudo virsh dommemstat fedora22-mig
> actual 2097152
> swap_in 0
> swap_out 0
> major_fault 1150
> minor_fault 356159
> unused 1689844
> available 2049328
> rss 496976
>
> This output says that the VM has 2097152 kB allocated and at the moment
> when command was executed, it was using 496976 Kb (the rss value).
>
> So, I looked for how those information is provided, and the Libvirt API
> provides all necessary information by the https://libvirt.org/html/libv
> irt-libvirt-domain.html#virDomainMemoryStats method.
>
> So, I'm going to work in this tasks and submit patch to provide the
> guest's memory usage in back-end. For the moment, I'm planning to
> return to following information:
>
> ### Resource: Virtual Machine
>
> **URI:** /plugins/kimchi/vms/*:name*
>
> **Methods:**
>
> * **GET**: Retrieve the full description of a Virtual Machine
>      * name: The name of the VM.  Used to identify the VM in this API
>      * state: Indicates the current state in the VM lifecycle
>          * running: The VM is powered on
>          * paused: The VMs virtual CPUs are paused
>          * shutoff: The VM is powered off
>      * stats: Virtual machine statistics:
>          * cpu_utilization: A number between 0 and 100 which indicates
>            the percentage of CPU utilization.
Since we are planning to provide virtual machine statistics, is it good 
idea to include cpu steal time of guest as part of this api? I see many 
of the cloud providers discussing on steal information and how that 
affects guest performance.

By the definition - Steal time is the amount of CPU time desired by a 
guest virtual machine that is not provided by the host. Steal time 
occurs when the host allocates these resources elsewhere: for example, 
to another guest.

If steal time exceeds certain %, it would need to revisit cloud set up, 
changing how cpu is getting shared or increase cpu for particular guest.

This feature will benefit customers using our product, to monitor and 
manage performance of guests .:-)

Here are some of the links which talks about steal time:
* 
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Virtualization_Deployment_and_Administration_Guide/sect-KVM_guest_timing_management-Steal_time_accounting.html

* 
http://blog.scoutapp.com/articles/2013/07/25/understanding-cpu-steal-time-when-should-you-be-worried

* http://www.stackdriver.com/understanding-cpu-steal-experiment/

* 
https://www.datadoghq.com/blog/understanding-aws-stolen-cpu-and-how-it-affects-your-apps/
> +        * mem_utilization: A number between 0 and 100 which indicates
> +          the percentage of memory utilization.
>          * net_throughput: Expresses total network throughput for reads
>            and writes across all virtual interfaces (kb/s).
>          * net_throughput_peak: The highest recent value of
>           'net_throughput'.
>          * io_throughput: Expresses the total IO throughput for reads
>            and writes across all virtual disks (kb/s).
>          * io_throughput_peak: The highest recent value of
>            'io_throughput'.
>      * uuid: UUID of the VM.
>
> Feedbacks are welcome.
> Best regards,
> --
> Paulo Ricardo Paz Vital
> IBM Linux Technology Center
>
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