Christian Elmerot @ One.com wrote:
Highest results comes at 32 threads: Number of Threads requested = 32 Function Rate (MB/s) Avg time Min time Max time Triad: 81013.5506 0.0378 0.0377 0.0379
There is some run-to-run variation in the results of this test, and accordingly some margin for error in each individual result. I wouldn't consider the difference between the speed at 32 threads (81) and 48 (79.7) to be statistically significant, and based on the overall shape of the results curve that 32 result looks suspicious. I would bet that if you run the test multiple times, you'd sometimes seen the 48 core one run faster than the 32.
The pattern is quite clear in that any multiple of 4 (the number of physical CPU packages) get a higher value but thinking about how the memory is connected and utilized this makes perfect sense.
In addition to the memory issues, there's also thread CPU scheduling involved here. Ideally the benchmark would pin each thread to a single core and keep it there for the runtime of the test, but it's not there yet. I suspect one source of variation at odd numbers of threads involves processes that bounce between CPUs more than in the more even cases.
-- Greg Smith 2ndQuadrant US greg@xxxxxxxxxxxxxxx Baltimore, MD PostgreSQL Training, Services and Support www.2ndQuadrant.us "PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
