Tuesday, January 11, 2011

Quantifying Our Westmere Turbo Mode Problems

MYSTERY SOLVED! (Jan 21, 2011): The throttling turned out not to be a processor flaw, though some minor bugs in the CPU or its documentation (not sure which) did contribute to a mis-diagnosis.  I can't state what was causing it, but it was not a flaw with Westmere or turbo mode. The issue was fixed by a simple iDRAC firmware update. More info.

This is a continuation of our search to find the cause of slowness with our Dell M610 blades using dual Intel X5650 Westmere processors.  Please see the other articles I have written, especially Flaws with Intel Westmere X5650?  The other relevant articles are Diagnosing Throttled or "Slow" Systems (Processors to be Precise) and Diagnosing Throttled Processors - Part 2.

During a maintenance window we were able to benchmark all of our systems.  We benchmarked our nodes multiple times with Intel's Turbo mode both enabled and disabled on the processors.  The results showed that 18% of our blades had worse performance with Turbo mode enabled than with it disabled.  That's 93 out of 515 blades included in the benchmark. These tests were done on Dell PowerEdge M610 blades with dual Intel X5650 Westmere processors (2.66 GHz) with 1066 MHz DDR3 DIMMs.  The graph below shows the result of the benchmark run with turbo mode enabled.

xhpl Linpack benchmark results in GFLOPS (rounded to the nearest integer) with turbo mode enabled.  Y-axis is number of blades. Each system is a Dell PowerEdge M610 with dual 2.66 GHz Intel Xeon X5650 processors with 24 GB 1066 MHz DDR3 RAM