[ovirt-devel] high performance VM preset

[Michal Skrivanek]

> On 24 May 2017, at 14:11, Francesco Romani <fromani at redhat.com> wrote:
> 
> On 05/24/2017 12:57 PM, Michal Skrivanek wrote:
>> Hi all,
>> we plan to work on an improvement in VM definition for high performance workloads which do not require desktop-class devices and generally favor highest possible performance in expense of less flexibility.
>> We’re thinking of adding a new VM preset in addition to current Desktop and Server in New VM dialog, which would automatically pre-select existing options in the right way, and suggest/warn on suboptimal configuration
>> All the presets and warning can be changed and ignored. There are few things we already identified as boosting performance and/or minimize the complexity of the VM, so we plan the preset to:
>> - remove all graphical consoles and set the VM as headless, making it accessible by serial console. 
>> - disable all USB. 
>> - disable soundcard. 
>> - enable I/O Threads, just one for all disks by default.  
>> - set host cpu passthrough (effectively disabling VM live migration), add I/O Thread pinning in a similar way as the existing CPU pinning.
>> We plan the following checks and suggest to perform CPU pinning, host topology == guest topology (number of cores per socket and threads per core should match), NUMA topology host and guest match, check and suggest the I/O threads pinning. 
>> A popup on a VM dialog save seems suitable.
>> 
>> currently identified task and status can be followed on trello card[1]
>> 
>> Please share your thoughts, questions, any kind of feedback…
> 
> In order to maximize performance we may also want to limit the number of
> other VMs (either regular or high performance) running on the same
> host. This to minimize the interference and the resource stealing.
> 
> 
> In the extreme case, just the selected high performance VM would be
> allowed to run on one suitable host.

well, it certainly goes in that direction. E.g. for a real time workloads/VMs the host needs to be configured in a way which makes it very cumbersome for other non-RT VMs - you need to reserve resources, typically you do not want to do that at all as when you are serious about performance or RT you really do not want any kind of overcommit.
Even for the most simple case of hugepages the pre-allocation of those pages seems to be the only reliable way of getting them for sure (at least for 1GB pages), and such memory is then unusable for non-hugepages VMs

> 
> Bests,
> 
> -- 
> Francesco Romani
> Senior SW Eng., Virtualization R&D
> Red Hat
> IRC: fromani github: @fromanirh
> 
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