On Friday 09 March 2012 08.44.53 Sorin Srbu wrote: ... > 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 compute 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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