O.T. : A nice app to see the raw power of your CPU : http://www.numberworld.org/y-cruncher/#Downloadmatthewlai wrote:The reason why Haswell's base clock is so low is mostly because of AVX.bob wrote:Actually Intel understates the speed. Running all 20 cores at once sees a constant clock speed of 2.9ghz. Only when you enable hyper threading and run 40 threads will it slow down to 2.6ghz. Running 3-4-5 threads and you will see 3.3ghz non-stop...Vinvin wrote:The v2 runs @2.2 GHz -> http://www.cpubenchmark.net/cpu.php?cpu ... 40+2.20GHzbob wrote:BTW this is a v3 chip:Joost Buijs wrote:TSX is disabled on all Haswell processors because there is an error in the implementation.ymatioun wrote:New Intel Xeon CPUs include something called "Transaction Synchronization Extensions".
I don't know exactly how they work, but those instructions were specifically designed to reduce synch overhead. Perhaps ICC emits those instructions, while GCC most certainly does not? That would explain why improvement only happens in parallel search.
I think the E5-2660v2 is a Haswell processor, the performance increase Bob sees must have an other explanation.
model name : Intel(R) Xeon(R) CPU E5-2660 v3 @ 2.60GHz
and the v3 runs @2.6 GHz -> http://www.cpubenchmark.net/cpu.php?cpu ... 40+2.60GHz
The limit is probably either power or thermal, and when you are not using AVX, half of the CPUs' floating point units are idle, and therefore they draw much less power.
By switching from SSE2 (128-bit) to AVX (256-bit) I get almost double the matrix multiplication throughput (and of course, if you are not doing floating point stuff at all, all FPs are idle).
If you run 20 threads of AVX-intensive workload, it will probably go down to the base clocks.
People (overclockers) have done a lot of tests to show that AVX very significantly increases power draw and temperature for Haswells.
It can use : AVX2, AVX, SSE4.1, SSE3, ...
Some records to break : http://www.numberworld.org/y-cruncher/#FastestTimes