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To hyperthread or not?

p4d hyperthread performance server

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#1 Miles O'Neal

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Posted 09 July 2020 - 10:38 PM

The only reference I could find to hyperthreading and Helix was a vague, minimalist KB article:

Our performance lab has tested the Perforce server with hyper-threading. The results indicate that hyper-threading does not improve Perforce server performance. While there is no evidence that hyper-threading has any negative impacts on performance, we recommend leaving hyper-threading disabled.

What, exactly, was tested? What were the results? Was the number of jobs ramped up past the number of physical cores with and without hyperthreading enabled, and no difference in results?

If there are no negative impacts, why leave it off?

Some actual results would be really nice. I realize that MMMV.

Has anyone here been involved in stress-testing p4d running on a modern (last year or so) server running RHEL7 (or any 3.x Linux), with and without hyperthreading? If so, what did you find?

We've been running hefty Intel-based servers with hyperthreading on the past 6-7 years with no obvious ill effects.

Thanks,
Miles

#2 Sambwise

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Posted 09 July 2020 - 11:44 PM

It's pretty rare for the Perforce server to be CPU-bound in the first place (at least in my experience -- there are probably unusual situations out there where CPU would be a limiting factor, e.g. massive map joins with the safeties off).  I suspect the "leave it off" recommendation is mostly a "if it ain't broke don't fix it" abundance of caution.

#3 Miles O'Neal

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Posted 13 July 2020 - 07:30 PM

Our hosts come configured with hyperthreading on, so I'll follow the "if it ain't broke, don't fix it" line of reasoning and leave them that way, 8^)





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