How do you measure TDP with a Kill-a-Watt? Energy consumption does not equate to thermal design power. Nor is TDP even a measure of peak thermal output ...
Sure it does, the energy has to go somewhere. If it's not being stored in some way or emitted as EM then heat is pretty much all that is left. If you measure voltage and current for Vcore going into the CPU then you can easily calculate the amount of heat it's generating since the CPU can't really store any appreciable amount of energy and there's basically nothing else that would allow that energy to leave the CPU.
Overall energy consumption of a computer does not equate to only the TDP of the CPU, itself.
Not really. Modern RAM uses a couple watts. Fans use at typical 2.5w each. Hard Drives only a few watts (SSD variety.) The PSU in servers tends to be fairly efficient, maybe losing 50-ish watts due to heat, and they run more efficiently at lower draws than higher draws. So using a Kill-A-Watt gives you a better idea of how much power the CPU is truly sucking down (especially when a GPU isn't installed.)
This is how I catch LED lighting companies lying about their actual power usage on their lights.
"TDP is not the maximum power that the processor can dissipate." -- Intel
Keep in mind that TDP is only a target number for typical use, not mprime. Not to mention Intel and AMD define it differently, see:
http://www.silentpcreview.com/article169-page3.html
"Intel is listing TDP numbers that are significantly lower than the actual maximum power draw of their CPUs."
That article is THIRTEEN YEARS OLD!
I mean, using that logic the max power consumption for the same six core processor Atwood tested would be around 280 watts. A number only 40 watts higher than his for heavy load. Too bad I used "false information" to reach such a usable number.
Now if the actual power consumption was double that, I'd definitely be berating Intel. But alas, no.
I get your point, but nothing wrong in drawing attention to the specs being incomplete to the point of being useless.
Have fun getting AMD and Intel to agree on something.
> I get your point, but nothing wrong in drawing attention to the specs being incomplete to the point of being useless.
Vague or averaged is not useless.
http://www.intel.com/content/dam/www/public/us/en/documents/...
Intel confusingly tells us "TDP: Thermal solution should be designed to dissipate this target power level. TDP is not the maximum power that the processor can dissipate."
So according to Intel [1] - "The best way to measure a server’s power consumption is the power meter, an inexpensive tool that is plugged into the wall, and then your device, like a server, can be plugged into the power meter. The meter displays the wattage drawn "at the wall" and allows you to analyze the power consumption under a variety of different utilization levels.". Strange.
I was looking up docs on AMD. They seem[2] to kinda get it: "To allow optimal reliability of the AMD Opteron and AMD Athlon 64 processor-based systems, the thermal and cooling solution should dissipate heat from a processor operating at its maximum thermal power.". I could find some old docs[3] that did give the maximum power, but can't seem to find any on their recent CPUs.
[1] http://www.intel.com/content/dam/doc/white-paper/resources-x...
[2] ftp://ftp.sgi.com/public/Technical%20Support/Pdf%20files/AMD/26633_5649.pdf
[3] http://hackipedia.org/Platform/x86/AMD/AMD%20Thermal,%20Mech...
4.1 T_CASE and DTS-Based Thermal Specification Implementation
Thermal solutions should be sized such that the processor complies to the T_CASE
thermal profile all the way up to TDP, because, when all cores are active, a thermal
solution sized as such will have the capacity to meet the DTS thermal profile, by
design. When all cores are not active or when Intel Turbo Boost Technology is active,
attempting to comply with the DTS thermal profile may drive system fans to speeds
higher than the fan speed required to comply with the T_CASE thermal profile at TDP.
In cases where thermal solutions are undersized, and the processor does not comply
with the T_CASE thermal profile at TDP, compliance can occur when the processor power
is kept lower than TDP, AND the actual T_CASE is below the T_CASE thermal profile at that
lower power.
In most situations, implementation of DTS thermal profile can reduce average fan
power and improve acoustics, as compared to T_CONTROL -based fan speed control. When
DTS < T_CONTROL , the processor is compliant, and T_CASE and DTS thermal profiles can
be ignored.
5.3.1 Intel ® Turbo Boost Technology
Intel ® Turbo Boost Technology is a feature available on certain Intel ® Xeon ®
processor E5-1600 and E5-2600 v3 product families SKUs that opportunistically, and
automatically allows the processor to run faster than the marked frequency if the part
is operating below certain power and temperature limits. With Turbo Boost enabled,
the instantaneous processor power can exceed TDP for short durations resulting in
increased performance.
(http://www.intel.com/content/dam/www/public/us/en/documents/guides/xeon-e5-v3-thermal-guide.pdf)
Intel literally spelled that out in this PDF which they linked from their TDP definition on every CPU specification page.
Now, in terms of power consumption. You must consider the entire system as the CPU is going to manage itself to fit its environment given the TCC. That is why Intel suggests you measure overall consumption for the server using a power meter as each implementation can yield different results. Therefore, what Atwood is doing is actually Intel's recommendation for considering actual power consumption. He, as I originally stated who knows how many replies ago, is making the mistake of directly equating power consumption to heat dissipation. When all you can really be sure of is that if a CPU consumes 1 watt of power it can dissipate up to the same in heat. But, as thermal dynamics will tell you, it will always be a bit less on the output as nothing is 100% efficient.
Therefore, all Atwood's test proves is an Intel® Xeon® Processor E5-1650 v3 has the potential to dissipate up to 250 watts of heat while in Turbo, given its recorded power consumption, in that specific computer configuration while running mprime. Nothing more, nothing less.
That is my point.
This is basic PSU and power supply principle.
The two CPUs were in identical test rigs. There is a 80W difference changing only the CPU. While you can expect some of this is lost in the PSU, simple fact is more power is ending up inside the computer and it has nowhere to go but out as heat. The most reasonable explanation given otherwise identical builds would be to expect this difference to be due to the changed component.
So if we assume that Intel's 4-core is actually 140W TDP, then there's no way this 6-core can also be 140W.
Yes, this isn't an exact, scientific test, but it's certainly reliable enough to say "this 6-core processor is emitting more heat than the 4-core, although they are rated identically" which it seems to me was the only point he was trying to make given the context which was "two more cores, slightly lower clock speed, that might be an okay tradeoff - OH WAIT, MORE HEAT".
Why? How can you say that under typical usage the thermal dissipation for both chips isn't the same? Atwood's numbers measure overall power consumption while idle and under heavy load with mprime, neither of which is what TDP seeks to measure.
TDP is like fuel economy for cars. You don't claim it's a lie when you go one hundred and fifty miles an hour for 20 miles and burn two gallons of gas. You simply realize those highway numbers are meant for more of a sixty mile per hour journey over the same distance.
Yes, TDP is an inexactly defined and meaningless term and while to the layman it would generally be understood to have some relation to the heat emitted by the CPU during normal operation, it's possible that both chips in fact only generate 1W of heat and were given a 140W TDP because Intel had a pre-existing cooling solution and a warehouse full of spare parts. Yes, you are correct on the semantics. Power consumption has no relation to TDP because heat generated has no defined relation to TDP.
However, given any meaningfully bounded definition of TDP, the case is still made that the TDP of these chips should be dissimilar. The later numbers show that under full load the power draw at the wall increases by 20W/core used. Unless your "typical load" used for determining TDP does not actually make use of the full number of cores (which I would think could be fine for a desktop processor, certainly not a server) then it's clear that the heat generated by these two processors should be dissimilar under any load.
If the 4 core actually needs to dissipate 140W under a typical use case, then the 6 core should absolutely need to dissipate more unless the "typical use case" is uselessly applied.
If we want to talk cars... Let's say I sell a base model with a top speed of 80mph, and a sport model with a top speed of 120mph. But I tell you you only need to put 80mph rated tires on the sport model because that's as fast as a typical person drives. Would you really claim that the sport model's tires are correctly rated? Would you not be surprised when you drove 100mph in the sport model and the tires exploded? Why on Earth would anyone even buy the sport model if it's crippled to nearly the same performance as the base model?
> Unless your "typical load" used for determining TDP does not actually make use of the full number of cores
> If the 4 core actually needs to dissipate 140W under a typical use case, then the 6 core should absolutely need to dissipate more unless the "typical use case" is uselessly applied.
Taken from Intel's own specs for the E5-1650:
"Thermal Design Power (TDP) represents the average power, in watts, the processor dissipates when operating at Base Frequency with all cores active under an Intel-defined, high-complexity workload. Refer to Datasheet for thermal solution requirements."
Immediately notice "Base Frequency", not Max Turbo, "all cores active", and "Intel-defined, high-complexity workload." Until you can perform the same test on both chips, you cannot assume that "these two processors should be dissimilar under any load."
In regard to your car analogy, if the sport version had a management interface to limit speed due to the rating on the tires, then it would be like an Intel CPU. Read this:
http://www.intel.com/content/dam/www/public/us/en/documents/...
Again, TDP is NOT peak thermal dissipation.
No. Different manufacturers use different definitions of what a typical load means.
> If not, how would you attempt to test it other than placing the processor under heavy load?
Well given that Intel has stated, "The TDP is not the maximum power that the processor can dissipate." Then testing under heavy load is most certainly not correct.
"Thermal Design Power (TDP) should be used for processor thermal solution design targets. The TDP is not the maximum power that the processor can dissipate."
"Analysis indicates that real applications are unlikely to cause the processor to consume maximum power dissipation for sustained periods of time. Intel recommends that complete thermal solution designs target the Thermal Design Power (TDP) indicated in Table 26 instead of the maximum processor power consumption. The Thermal Monitor feature is intended to help protect the processor in the unlikely event that an application exceeds the TDP recommendation for a sustained period of time."
Therefore, are Atwood's test results really a shock? At idle both chips are within 15 watts of each other, yet under sustained load (which is not what TDP seeks to measure) they both violate their advertised TDP.