Intel’s Sandy Bridge i7-2820QM: Upheaval in the Mobile Landscapeby Jarred Walton on January 3, 2011 12:00 AM EST
Performance and Power Investigated
Given all the performance packed into the i7-2820QM, worst-case heat and noise levels should still be similar to what we encountered with Clarksfield. Idle power is good, but if you want to do some heavy processing or gaming what happens? We connected the Compal system to a Kill-A-Watt device to check power draw under various loads, as well as testing battery life while looping a graphics intensive application. We’ve seen NVIDIA and AMD GPUs really curtail performance on DC power, but has Intel done the same?
We’ve created a table of power draw at the outlet for several usage scenarios, as well as the calculated power requirements on DC based on the 71Wh battery. We’ve also included the performance figures for the tasks where applicable, to see if performance throttling is in effect when on battery power. We used the “Balanced” power profile for the AC tests, and the Power Saver profile (but still allowing the CPU to go to 100%) for battery tests. For the graphics test, we enabled the “Maximum Battery Life” setting as well as the “Balanced” setting—the graphics tests on AC were done using the “Maximum Performance” setting.
|Power/Performance Under AC/DC|
Power at Outlet /
Calculated DC Power
|3DMark06 (DC) MaxBat||23.61W||2800|
|3DMark06 (DC) Balanced||41.18W||5184|
|H.264 Playback (DC)||16.38W||N/A|
|Cinebench 11.5 SMP||70-89W||5.72|
|Cinebench 11.5 SMP (DC)||59.17W||5.09|
Watching power draw and CPU clocks (using CPU-Z) during the tests was rather interesting. There’s not much going on in the idle test; looking at the numbers, AC power use is about 36% higher than the DC calculated power use. Most likely extra power-saving features are in effect under DC power.
In the Internet test (under AC), while the web pages are loading the system used anywhere from 18-31W. Once all four pages have finished loading, however, power would settle down to 14W—just slightly higher than the idle power draw. That’s quite impressive, given the Flash content on the active page, and that’s reflected in the only slightly higher calculated power draw for Internet battery life vs. idle. Also of note is that the CPU clock speed never even hit 2.3GHz—let along the maximum 3.4GHz—during the Internet test, at least not that we could detect. We could see it reach 1.6GHz for a few seconds, and then it would settle back to 800MHz.
The H.264 playback test is another example of low CPU clocks and utilization through the test. The initial loading of the x264 movie would bump clock speeds up, but then the CPU would drop back to the minimum 800MHz and stay there. Power draw is definitely higher than the idle/Internet tests, but 20-21W isn’t too shabby for a 17.3” notebook. And then we get to the power hungry tests, simulating gaming and heavy CPU use.
3DMark06 power requirements are generally similar to gaming results, with the wide spread being typical. Tests 1, 3, and 4 averaged power draw closer to 53W, while test 2 (the Firefly Forest) was nearly 10W higher on average. Turbo Boost—on both the CPU and GPU—is very likely in play, but we didn’t have a good way of measuring real-time clock speeds during the tests. We tested battery graphics performance using two settings; first is the “Maximum Battery Life” setting, which results in roughly half the performance compared to running on AC. The second mode is labeled “Balanced”, which improves the score quite a bit—at the cost of power consumption.
Based on the 3DMark06 results, plugging in improves graphics performance by 2-82%, depending on what graphics power saving setting you select. You’ll definitely want to run the higher performance GPU mode if you actually want to play games, as otherwise frame rates will drop into the low 20s or upper teens on most titles. With the “Balanced” or “High Performance” GPU setting, gaming performance is reasonable even on battery power, but it puts enough of a load on the battery that you won’t be able to last more than around 90-100 minutes. If you happen to have a game where you only need the power saving performance mode, though, you should be able to get gaming battery life up to three or perhaps even four hours (depending on the game).
Finally, we’ll wrap up this discussion by looking at maximum CPU loads. In the Cinebench test, quad-core Turbo is interesting to watch; running the CB11.5 SMP benchmark, at first all of the cores start at the maximum 3.10GHz speed—blisteringly fast for a notebook! About 11 seconds in to the test, the core speed drops to 3.0GHz, where it remained until 39 seconds; then it dropped to 2.9GHz, and at around 54 seconds the speed dropped briefly (1-2 seconds) to 2.8GHz before settling in at 2.7GHz for the remainder of the test. If you happen to run heavily-threaded benchmarks continuously, the first run will usually show about 10% higher performance thanks to the initial thermal headroom, but the lowest Cinebench SMP and x264 encoding scores that we measured are still within 10% of the maximum score, which is very impressive for notebook hardware.
At the highest point in the test, power draw for the notebook peaked at 89W; once the speed settled at 2.7GHz (which it appears the notebook could sustain indefinitely in our 70F testing environment), power draw was steady at 70W. Switch to battery power and the Power Saver profile, and performance did drop slightly but not as much as you’d expect. We measured 5.09 PTS while running off the battery, so plugging in nets you up to 12% better performance. Like gaming, battery life under a heavy CPU load is going to be much lower than our other tests, and we measured just 72 minutes. Then again, compare that with some of the other high-end notebooks we’ve looked at in the past, which managed a similar 72 minutes with no load whatsoever.
One thing to keep in mind is that the effectiveness of Intel’s Turbo Boost technology does depend on the cooling equipment. While the Compal sample runs reasonably cool—we’ll check temperatures on the next page—we have definitely seen larger, more robust cooling solutions. The profile of the Compal chassis is generally flat, so that limits the size of the fan(s) and the amount of airflow. Something like the ASUS G73 chassis has proven quite effective at running high-end mobile components in the past, and we suspect that better cooling will result in the CPU running closer to the maximum Turbo limits more of the time. We’ll have to wait for sample notebooks to confirm our suspicions, but we’ve seen it in the past with Clarksfield and Arrandale, so there’s no reason Sandy Bridge would behave differently.