In a given CPU family Intel sells CPUs at a variety of frequencies that have the same TDP. As far as I understand it for Sandy Bridge CPUs:
Ultimately, I guess the main question is: Do the two higher end 115W TDP chips really run appreciably faster than the 2665 for sustained workloads stressing all 8 cores or do they simply offer higher short term performance and higher performance when only a few cores are loaded?
Then the next logical question is: Can the E5-2689 really offer the same performance under a long term 8 core load as the E5-2690 despite a 20W lower TDP? Both are supposedly capable of 3.3gHz turbo on all 8 cores if Wikipedia is correct. That seems hard to believe unless the E5-2689 has a better "bin" of silicon with much better VID vs. frequency characteristics than the E5-2690.
I read through this Intel presentation, but it doesn't really answer my questions. I did glean from it that the sustained clock frequency (once the TDP limit is being enforced) can exceed the base clock, but isn't guaranteed. It makes the whole thing seem like a big, "Well, it depends..." with a lot of potential chip to chip variation even with two identical model CPUs.
Can anyone explain to me how this works, or point me to something that explains this?
- The BIOS/motherboard/processor will enforce the TDP limit, but allows the CPU to temporarily exceed by 1.2-1.3x it for some amount of time.
- With everything else being equal power consumption increases as frequency goes up.
- TDP != power consumption
- Xeon E5-2665 has a base clock of 2.4gHz and turbo limits of 4/4/5/5/6/6/7/7 with a TDP of 115W
- Xeon E5-2670 has a base clock of 2.6gHz and turbo limits of 4/4/5/5/6/6/7/7 with a TDP of 115W
- Xeon E5-2689 has a base clock of 2.6gHz and turbo limits of 7/7/7/7/8/8/10/10 with a TDP of 115W
Ultimately, I guess the main question is: Do the two higher end 115W TDP chips really run appreciably faster than the 2665 for sustained workloads stressing all 8 cores or do they simply offer higher short term performance and higher performance when only a few cores are loaded?
Then the next logical question is: Can the E5-2689 really offer the same performance under a long term 8 core load as the E5-2690 despite a 20W lower TDP? Both are supposedly capable of 3.3gHz turbo on all 8 cores if Wikipedia is correct. That seems hard to believe unless the E5-2689 has a better "bin" of silicon with much better VID vs. frequency characteristics than the E5-2690.
I read through this Intel presentation, but it doesn't really answer my questions. I did glean from it that the sustained clock frequency (once the TDP limit is being enforced) can exceed the base clock, but isn't guaranteed. It makes the whole thing seem like a big, "Well, it depends..." with a lot of potential chip to chip variation even with two identical model CPUs.
Can anyone explain to me how this works, or point me to something that explains this?