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Re: IRQ latency measurements in hypervisor

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.


Julien Grall



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