Re: HT on or off for E5-26xx ?

On 11/7/2012 6:37 AM, Devrim GÜNDÜZ wrote:
> HT should be good for file servers, or say many of the app servers, or
> small web/mail  servers. PostgreSQL relies on the CPU power, and since
> the HT CPUs don't have the same power as the original CPU, when OS
> submits a job to that particular HTed CPU, query will run significantly
> slow. To avoid issues, I would suggest you to turn HT off on all
> PostgreSQL servers. If you can throw some more money, another 6-core CPU
> would give more benefit.
I realize this is the "received knowledge" but it is not supported by 
the evidence before me (which is that I get nearly 2x the throughput 
from pgbench using nthreads == nhtcores vs nthreads == nfullcores). 
Intel's latest HT implementation seems to suffer less from the kinds of 
resource sharing contention issues seen in older generations.

Once I have the machine's full memory installed I'll run pgbench with HT 
disabled in the BIOS and post the results.