...
What are some of the cases it would be practical/best to have it off?
I know there might be some negative performance issues with certain
applications, but would you notice it in day-to-day use?
Negative performance due to HT comes in several flavours. Some computeI know there might be some negative performance issues with certain
applications, but would you notice it in day-to-day use?
intensive loads simply perform a bit better with HT off (usually measureable
but not really noticeable, 1-10% is expected here). Another way HT can cause
you performance degradation is due to incorrect scheduling and/or pinning.
What happens then is that two threads are (incorrectly) put on the same core
instead of using two cores (impact: ~half performance).
On the positive side, if you have many (preferably independent) threads you'll
often get both better throughput and better system response/latency (more
"processors" available for the kernel to schedule on).
/Peter
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