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I am running a couple of Debian 6 (2.6.32) and 7 (3.2) Linux servers and all of them have energy saving settings enabled in their BIOS. Furthermore Linux shows that the CPUs are throttled if the servers are idling.

I wonder if this could cause any harm - could there be e.g. performance impacts because Linux would not be able to handle throttling correctly?

Is there a best practice for Linux servers and power/CPU throttling? Do you guys switch your energy profiles to "performance" or do you leave both the BIOS and the OS with their default settings?

The reason I am asking is that I encountered several performance issues on physical Dell servers although all values (CPU/load, memory, I/O, network etc.) seemed to be normal. After changing the BIOS power settings to "performance" in those specific cases, I was able to get rid of the performance issues.

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3  
Looks much the same as serverfault.com/q/94212/126632 to me. –  Michael Hampton May 27 at 14:54
    
Thank you for the link. I searched Google and this site several times, but for some reason I didn't find this specific question. But still I would like to hear Linux-specific replies. –  Valentin May 27 at 15:13
1  
@Valentin It's not a duplicate, but I'm not sure what additional information you need. –  ewwhite May 30 at 12:32
    
I appreciate your answert and your comment. However, I would like to hear more opinions on the subject (also links/sources regarding experiences with this topic would be great). Furthermore a clear reply like "yes, performance mode in BIOS means better performance" or "performance mode in BIOS does not have an impact on performance" would be helpful. Again, I still thank you for your answer, I am just missing more information/opinions/experiences. –  Valentin Jun 2 at 10:17
    
@Valentin It depends on what you're doing with the server and how you define performance. Of course "High Performance mode" would translate into better potential CPU performance. But that's not the only metric professionals use to assess system performance. I gave three specific use cases and their respective power settings. It sounds like you solved your issue with a BIOS power settings change. –  ewwhite Jun 2 at 15:28

2 Answers 2

Interesting question...

In general, I base the system performance profile on the application and intended use of the server. I typically work with:

  • Low-latency transaction-heavy systems.
  • Virtualization hosts (VMware).
  • Linux-based ERP servers.

The systems that require deterministic performance and low-latency are typically set to a high-performance profile, disabling all C-States/P-States and any power throttling.

The Virtualization hosts can follow the same model, but if I'm power-constrained (like in a co-location facility) or the workload is minimal across the hosts/cluster, I will leave the default balanced power/performance profile enabled. That's typically because I'm charged for power and cooling in a data center, and may need to be able to consolidate more physical servers into a given footprint.

The ERP servers are typically standalone. Lighter workloads get the default balanced profile. Systems that require more specific tuning and have a heavier workload (24x7 operation) may see high-performance power profiles applied.

-- edit --

Again, performance tends to be more deterministic under the high-performance power profiles. It really depends on your specific application and what your users are experiencing (we can't tell you what to do). You state yourself that disabling the BIOS power-saving features corrected a performance problem you were having.

For Linux, download the PowerTop utility and experiment to understand what your CPUs are doing under realistic workloads.

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up vote 0 down vote accepted

I think it might be a benefit for others stumbling accross this question if I post my latest knowledge gain here as a reply.

I talked to Dell and Intel since in my specific situation, Linux is not able to scale up throttled CPUs again in certain situations. Dell replied that this issue is known and occurs both with VMWare hypervisors and many Linux variants, so it is not Debian or Dell model specific. As far as I can tell, all Dell systems using Intel CPUs can be affacted and of course it is also possible that other hardware vendors share this problem.

Dell claims in a mail written in German:

  • Linux fails to negotiate power settings with the hardware in my specific cases
  • Updating both the OS and firmware might help
  • Using the "Performance" profile is a known workaround

Looking at Dell's mail it seems that there is no way to fix this, only a workaround. Therefore the reply to my own question would be:

In order to prevent possible performance or CPU scaling issues with your servers, I highly recommend to put all your servers in the datacenter into "max. power" mode.

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