[ClusterLabs] FYI: Performance impact of recent fixes for Intel CPUs (SLES11 SP4)

[Ulrich Windl]

Hi!

After some recent changes that also included installing the fixes for Intel CPU defects, I've noticed some disk performance degradation (SLES11 SP4). Unfortunately there were too many changes done to isolate the effect of the software patches.
Yesterday I just installed the recent fixes, and the effect of performance degradation is visible. Most interestingly it's the fastest I/O that suffers most ("emin").

Attached is an image showing minimum, maximum and average read access time to a FC-SAN storage system before and after the updates. The whole maintenance was done in about six steps lasting from 14:20 to about 16:00 (marked with a yellow box).

Notes: min and max are exponentially decaying; otherwise these values would be quite boring.
If you look closely, you'll see that the average suffered a bit also.
There was no microcode update for the CPU (Xeon 5650 stepping 2) yet.

Docs stated that performance degradation would be visibly with SSDs mostly. Maybe it's because the I/O delays are very low there, too.

Regards,
Ulrich


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