Intel® Xeon Phi™ coprocessor Power Management Configuration: Why should I worry about configuring anything?

Previous blogs on power management and a host of other power management resources can be found in List of Useful Power and Power Management Articles, Blogs and References.

WHAT AND WHY DO WE WANT TO CONFIGURE IT

There are several reasons why you might want to configure your power management in different ways. For example, you may want to disable turbo due to the sensitivity of your application to OS jitter. The table below lists some of the reasons you might want to change a power setting.

Power setting change

Reason

Turbo off

  1. Your application is particularly sensitive to OS jitter
  2. Your cluster cannot exceed a certain fixed power ceiling
  3. Your application needs a constant frequency (meaning it is sensitive to variations in the frequency of the processor)

Turbo on

  1. You want your application to get every performance boast that is possible
  2. Your application has (relatively) frequent periods of “rest” such that turbo has the potential of providing a significant performance boost.

PC6 enable

  1. Your application has no special thermal or latency requirements
  2. Your application has long periods of inactivity
  3. Your cluster has a low thermal ceiling and relatively long periods of coprocessor inactivity

PC6 disable

  1. Your application cannot tolerate the high latency inherent in reactivating an application between periods of low activity
  2. Your application cannot ignore coprocessor directed PCI events

PC3 enable / disable

Examples similar to that of PC6 enable/disable with the exception of PCI events. Latency dramatically increases once you drop into PC3 since the part of the coprocessor power management module that is on the host needs to initiate an exit from PC3 back to C0.

P1 enable / disable

  1. The cooling capability of your host/coprocessor system needs to be “smoothed” to avoid thermal spikes (enable)
  2. Your application has no special thermal requirements (enable)
  3. Your application needs a constant frequency, meaning it is sensitive to variations in the frequency of the processor (disable)

CO6 enable / disable

  1. Your application is particularly sensitive even to short latencies (disable)
  2. Your application has no special thermal or latency requirements (enable)

 

In a smaller cluster, you may want to experiment with enabling versus disabling turbo. Enabling or disabling various power management states may give you some performance gain for specific workloads.

If you are designing a large cluster, you may want to disable turbo because it may increase the headroom your thermal extraction system (e.g. air conditioning) needs to support the coprocessor. This can be the case even if the average meets your specifications.

NEXT: Intel Xeon Phi coprocessor Power Management Configuration: Using the micsmc GUI

REFERENCES

Kidd, Taylor (2013, October) List of Useful Power and Power Management Articles, Blogs and References, revision 1.0, Intel® Developer Zone website, Intel® Corporation, http://software.intel.com/en-us/articles/list-of-useful-power-and-power-management-articles-blogs-and-references

 

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