Re: [Xen-devel] xen 4.5.0 rtds scheduler perform poorly with 2vms

[Meng Xu <xumengpanda@xxxxxxxxx>]

2015-11-27 12:23 GMT-05:00 Dario Faggioli <dario.faggioli@xxxxxxxxxx>:
> On Fri, 2015-11-27 at 08:36 -0800, Yu-An(Victor) Chen wrote:
>> Hi Dario,
>>
> Hi,
>
>> Thanks for the reply!
>>
> You're welcome. :-)
>
> I'm adding Meng to Cc...
>

Thanks! :-)

>> My goal for the experiment is to show that xen rtds scheduler is
>> better than credit scheduler when it comes to real time tasks.
>> so my set up is:
>>
>> for xen-credit : 2vms sharing 8 cores (cpu 0-7) using credit
>> scheduler(both with weight of 800 and capacity of 400)

So you set up 400% cpu cap for each VM. In other words, each VM will
have computation capacity almost equal to 4 cores. Because VCPUs are
also scheduled, the four-core capacity is not equal to 4 physical core
in bare metal, because the resource supplied to tasks from VCPUs also
depend on the scheduling pattern (which affect the resource supply
pattern) of the VCPUs.

>> for xen-rtds: 2 vms sharing 8 cores (cpu0-7) using RTDS (both with
>> period of 10000 and budget of 5000)

How many VCPUs  for each VM? If each VM has 4 VCPU, each VM has only
200% CPU capacity, which is only half compared to the configuration
you made for credit scheduler.

>> in both setup, dom0 is using 1 core from cpu 8-15

Do you have some quick evaluation report (similar to the evaluation
section in academic papers) that describe how you did the experiments,
so that we can have a better guess on where goes wrong.

Right now, I'm guessing that: the resource configured for each VM
under credit and rtds schedulers are not the same, and it is possible
that some parameters are not configured correctly.

Another thing is that:
credit scheduler is work conserving, while RTDS is not.
So under the under-loaded situation, you will see credit scheduler may
work better because it try to use as much resource as it could. You
can make the comparision more failrly by setting the cap for credit
scheduler as you did, and running some background VM or tasks to
consume the idle resource.

Meng

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