C-States

[b1izzard]

Does anyone know if setting the 'Minimum Processor Idle Power Core State 'BIOS setting to 'No C-states' in HP Proliant servers is recommended or a bad idea?  I can't think of a reason why it would cause an issue, but thought I would solicit some feedback before making changes willy nilly.  Thanks.

[bluefirestorm]

Interesting two bullet points on page 18.

https://www.vmware.com/content/dam/digitalmarketing/vmware/en/pdf/techpaper/performance/Perf_Best_Practices_vSphere65.pdf#page=17&zoom=auto,-388,263

From one of the bullet points

However, for a very few multithreaded workloads that are highly sensitive to I/O latency, C-states can reduce performance. In these cases you might obtain better performance by disabling them in the BIOS.

Is that the reason you are looking to disable C-states altogether?

I think the C6/C7 states are supported by Haswell and newer CPUs. Support of C-states may also vary according to power supply.

[b1izzard]

Yes, I was thinking about disabling C-States altogether.  I was reading through this article on improving server performance and was wondering what the potential impact would be when he says to set the BIOS to Minimum Processor Idle Power Core State - No C-states.

Easy ways to boost the performance of HP Proliant servers, that you might not know

[bluefirestorm]

Well, for sure disabling C-states will increase power consumption. Whether it will result in an obvious performance gain, I think it is debatable.

Disabling C-states would mean the CPU will never lower its power draw and will maintain its base clock speed even when it is idle. Constant power draw also means higher CPU temperature and a constant higher temperature could possibly lead the CPU to top out its performance sooner. It could lead to the CPU reaching its TDP/Tjunction/Tcase max sooner when the real need for CPU speed kicks in, versus with C-state enabled it started with a lower temperature base and it will take slightly longer to reach it, if at all.

You can make this same observation with a Windows desktop/laptop set to "High Performance" profile (in Windows OS setting), the clock speed of all CPU cores will never go down and it will lead to a higher idle temperature, higher speed spin of the fans.

[Scott Vessey]

Wouldn’t this be a question for a HP forum?

[b1izzard]

I asked here in case there is some reason related to ESXI that you should not do this, as in power management.