Hyperthreading - Yes or no? Experiences?

[Rudi_Wiesmayr]

Hi!

What about switching on hyperthreading on older CPUs?

There are very ambiguous "recommendations" one can hear...

Some say: If the processor can, switch it on.

Others say: SAP is not prepared for hyperthreading, so switch it off.

What may be the truth?

And what are the technical arguments?

What are your experiences?

Kind regards, Rudi

And: Don 't mix this up with dual core CPUs...

[christoph_volkert]

as told in

https://www.sap.com/documents/2016/09/2cbf0206-8a7c-0010-82c7-eda71af511fa.html

If you compare the SAME amount of physical cores, with the SAME amount of pysical cores + HT (= double amount of logical cores) then you can get a perdormance boost up to 10-30%.

Of course, if you compare e.g. 8 vCPUs to 8 pCPU, the vCPU setting will be much slower, as you only use the half amount of pCPU.

[Former Member]

Hi Rudolf,

SAP is a single threaded application. Each work process can affinitize to only one CPU, or more correctly OS thread.

With Hyperthreading 2 logical threads are presented to the OS for each physical core. Each of these threads has approximately half the SAPS of the physical CPU/core. Therefore long running CPU intensive batch jobs perform worse with hyperthreading.

There is no clear rule - you need to test your specific environment with your specific workload.

For SQL server the rule is simple. ALWAYS switch it off.

http://blogs.msdn.com/slavao/archive/2005/11/12/492119.aspx

Interesting to see what comments come up in this thread.

N.P.C

[markus_doehr2]

We have had likewise experiences. On a database server it´s recommended to switch off - on pure application servers, that do NOT do longrunning batchjobs, HT may be switched on but you won´t see a significant performance gain - that´s at least what we saw.

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Markus