Re: IRQ latency measurements in hypervisor

[Julien Grall <julien@xxxxxxx>]

Hi Stefano,

On 15/01/2021 23:17, Stefano Stabellini wrote:
> On Fri, 15 Jan 2021, Volodymyr Babchuk wrote:
> > 9us was in idle state. Interestingly enough, I got latency if 3us while
> > Dom0 was doing some CPU-intensive tasks. So, under load latency is lower
> > than in idle state. I didn't investigated this, so I can't tell you what
> > causes this behavior.
> Did you use vwfi=native? You should definitely be able to see ~3us
> without interference and with 1vCPU <-> 1pCPU
vwfi=native works well in a scenario where each pCPU is dedicated to a 
vCPU. However, if you start to oversubscribe the pCPU, the performance 
are going to degrade quite a lot because there will be less opportunity 
to schedule a different vCPU.
You will also waste quite a bit of pCPU cycles because the vCPU will sit 
doing nothing until the end of its time slice.
Cheers,

--
Julien Grall