Dell XPS 15 L521X: A Detailed First Look
by Jarred Walton on July 25, 2012 1:10 AM ESTDell XPS 15 Thermal and Throttling Investigations
Considering the CPU throttling that’s occurring with the current BIOS, we have several sets of data to examine. We logged clock speeds and temperatures on the CPU and GPU using HWiNFO64, and we’ll analyze the results here. Let’s start first with the system running “stock” with the A04 BIOS. Again, the current results likely do not represent exactly what we’ll see from future BIOS revisions, but I expect temperatures will be somewhere between the stock and ThrottleStop figures we’ll discuss in a moment. For the stress testing that we’re doing here, we loaded up Cinebench 11.5 rendering with three threads (looped), and we ran 3DMark06 at 1080p on the four gaming tests in a loop. There are slight gaps that occur each time one test ends and the next begins, so a short-term drop in clock speeds isn’t particularly noteworthy; it’s only when we see sustained lower clock speeds that we can clearly state that the system is throttling.
Starting with the clock speeds, it’s immediately obvious how far the CPU is throttling and how significant the problem is. With our stress test workload we’re able to hit the thermal limits (around 80C on the CPU) in just 30 seconds, at which point the CPU drops to 1.2GHz from 2.8GHz. While our graph only shows the first couple of minutes, the 1.2GHz clock remained in effect for over five hours of stress testing, with nary an upward spike until we halted the tests. Most of the time, we were able to run this workload without problems, but we did experience at least one crash. There’s also the question of what would happen under more extreme environmental conditions, as our testing was done in a 70-73F AC cooled environment. Here’s a look at the temperatures for the CPU cores and GPU at stock:
With our particular workload, we reach a maximum CPU temperature of 88C after 20 or so minutes, at which point the cyclical nature of our workload causes the CPU/GPU to fluctuate between 79C and 88C every six or seven minutes (the length of time for a complete 3DMark06 loop). The GPU reaches a maximum temperature of 85/86C after 40 minutes, and again temperatures fluctuate depending on the workload between 76C and 85C over the course of six or seven minutes. A more difficult workload (e.g. Furmark with OCCT) might present problems, but we’re looking at a more realistic scenario and at least the thermal throttling keeps the laptop from crashing.
Running stock is well and good for many, but can we push performance any higher by increasing the CPU clocks? That’s what we attempted to do, and we turned to ThrottleStop for this purpose. Having successfully run all of our gaming suite at 2.3GHz using ThrottleStop, that’s where I started the stress testing. I was a little surprised when the laptop shut down after just 7.5 minutes. Ouch! The CPU cores top out at 100C and the GPU hits 93C, with the laptop sustaining those temperatures for about 30 seconds before crashing (powering off with no warning). With that result in hand (and confirmed with a couple of retests), I stepped the CPU clock back to 2.1GHz. With 200MHz knocked off the CPU clocks, the stress test ran successfully for 20 minutes before once again crashing, and this time the CPU cores maxed out at 99C with the GPU again reaching 93C. The laptop managed to run for five minutes after the first instance of those temperatures, so we’re at least heading in the right direction.
Next up I tried 2.0GHz, thinking I was getting close to “stability”, and the XPS 15 ran for just over an hour before it crashed once again. Maximum CPU temperatures dropped to 98C and the GPU topped out at 92C, but we’re not quite there yet. Interestingly, 1.9GHz on the CPU didn’t do any better, with crashes occurring after 45 to 60 minutes three times before we gave up, and similar max temperatures. At 1.8GHz, we finally reached relative stability, with the XPS 15 handling our looped workload for over four hours. The maximum CPU temperature at 1.8GHz was 95C, and the first time it reached that temperature was just over an hour into the stress test, with the core temperature cycling between 89C and 94/95C every six or so minutes. The GPU maximum temperature was 89C, cycling between 84C and 89C. We put together charts of the CPU/GPU temperatures for our four test runs and you can see them in the following gallery.
As for the system itself, surface temperatures are significantly lower than the CPU and GPU core temperatures reported by HWiNFO, and the chassis never felt uncomfortably hot in our experience—the silicone coating on the bottom helps in this regard, though it may also be inhibiting the radiating of heat through the chassis and contributing to the higher temperatures.
Noise levels are relatively loud (I’d guess around 40dB—I don’t have my SPL meter with me right now), but given the throttling issues the fan should really be spinning faster to compensate—and apparently it can’t. Also note that the exhaust is located under the LCD hinge, which is potentially exacerbating the issue. If the airflow weren’t inhibited by the LCD/hinge, it’s possible the temperatures would drop 5C or more, which might be enough to avoid most of the throttling problems. At idle, noise isn’t a problem at all, with the XPS 15 typically coming in at or below the noise floor of our equipment (30dB). I’d personally rather have a laptop that gets louder but doesn’t overheat, throttle, or even worse crash than a laptop that runs quietly but experiences all of those problems. Of course, in an ideal world you could get both reasonably quiet as well as high performance, but doing so with a thin laptop chassis isn’t in the cards right now. We’ve seen the same issues with throttling (or at least lower clocks) on most of the Ultrabooks we’ve tested as well.
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air_ii - Thursday, July 26, 2012 - link
Given current fan / throttling profiles, wouldn't it be interesting to see gaming performance of a throttled i7/GF vs nominal (or perhaps turboed?) IGP performance? Perhaps the GF is completely pointless under circumstances?TC2 - Thursday, July 26, 2012 - link
The best for the Best :) It's an excellent machine!TheTechSmith - Thursday, July 26, 2012 - link
"And on a related note, I should mention that I’ve seen at least some minor throttling with several other “thin but fast” laptops, so Dell’s not alone here; we’ll be making a concerted effort to check for throttling on all future laptop reviews."Yes! I think this is a great idea. I've believed for years that laptops like the one that you just reviewed have been slapped together without proper thermal design (lack of the required mechanical knowledge, reluctance to put in the required money/time?) in order to sell it on specs, and the end result is terrible, and I don't think there is enough awareness on this issue. I posted a little earlier on my XPS M1330 which is a 4 year old computer with the same issue. If reviews start testing for this specifically and compare laptops quantitatively against other laptops (temperature and average frame-rate of select games over time?), then perhaps companies that are poor in this area will hire the required mechanical engineers and dedicate the proper money and time to do it right.
SovereignGFC - Thursday, July 26, 2012 - link
On page 7, it was noted the laptop shut down under load after ThrottleStop was used to force it to run at a specified speed rather than the BIOS-controlled throttled speed.According to Intel (http://ark.intel.com/products/64901), this CPU is rated for a TJunction (maximum core temperature) of 105C. The CPU only hit 100C during these tests, so that implies to me that CPU temperature, while VERY high, was within spec and should not have triggered a shut-down.
If the GPU hit its limit, that's a different story.
However, as an owner of an XPS1640, well-known for behaving similarly, I have to ask whether the A/C adapter Dell shipped is adequate for such a powerful machine. The A/C adapter was sized based on the machine being throttled, not unlocked the way ThrottleStop will permit it to run. I can offer at least one anecdote (many more can be found on NotebookReview's forums) about A/C adapter vs. thermals. This throttling was present in the Latitude E6X00 series of professional notebooks, one of which is owned by a friend. After showing him how he wasn't getting the performance he paid for, he un-throttled his CPU and ran Prime95 to test its thermals.
The machine shut down in a few minutes and the A/C adapter was too hot to touch for a while afterward.
Many XPS1640 owners reported that calling Dell, mentioning "throttling" and asking for a 130w A/C adapter allowed their machines to run properly under "full load." Even though components would be subjected to high heat (I've seen 103C on my Core 2 Duo, 88C on the GPU) they would also receive enough energy to operate as designed, rather than stressing or even destroying the A/C adapter in the process.
JarredWalton - Thursday, July 26, 2012 - link
I can't test this right now, but the thought that we might be exceeding the power limit did cross my mind. I don't think that's the case, however, as there are various triggers that can cause a system to shut down. I'm guessing Dell defined a maximum temperature of some other component, or that something on the motherboard is overheating. I'll look into power draw when I return home next week.SovereignGFC - Thursday, July 26, 2012 - link
Thanks.What annoys me the most is that we get these half-crippled machines that emphasize form over function. I don't care if it looks like a brick--it's a gaming machine and gaming machines need to dissipate huge amounts of heat.
http://forum.notebookreview.com/dell-xps-studio-xp... - That's a massive discussion about heat/power throttle on the 16XX series.
http://forum.notebookreview.com/dell-xps-studio-xp... - People are already talking about the L521X negatively, "it throttles so badly under a realistic gaming load that I'm returning it."
That said, I don't see any "load" (power) related throttling mentioned.
CeriseCogburn - Sunday, July 29, 2012 - link
Yes, good points.Doesn't matter if this site's is under performing from the lack of adequate ps as that is what end users will be receiving, except in the sense it would be nice to know. It certainly wouldn't surprise me if it was. I doubt they're going to purchase a 130W universal adapter to find out.
Great points, I agree with you, the insane emphasis on looks bothers me as well - it's even worse in discrete video cards, as you won't be staring at them as you game - with a laptop I can excuse quite a bit of it - as you will be looking at it a lot.
SovereignGFC - Monday, July 30, 2012 - link
If enough people complain (like the XPS 16), Dell will give out 130w adapters like candy, even though by themselves they did not solve the problem with the XPS 16. Only completely cutting the BIOS out of the CPU equation and replacing it with ThrottleStop let my laptop run like it was supposed to.If tests on sites like Anand say "This laptop needs MO' POWAH!" then Dell will probably jump at a cheap "fix." I'm not saying we know for sure a larger adapter is required (that's what the tests will be for) but experience suggests power may be a factor.
JarredWalton - Thursday, August 9, 2012 - link
Just to update (and spoil the surprise): I plugged the XPS 15 into a 135W Dell adapter; throttling still occurs just as quickly as before, so it's not a power adapter problem.JNo - Thursday, July 26, 2012 - link
I think the Acer M3 looks might tempting value when looking at the graphs. It's got about 90% of the power for about 50% of the price. Sure it's not all about specs and Acer's build quality and looks are nowhere near that of the Dell but I can't ignore that price differential.So what are you really missing out with the Acer? Two things spring to mind: 1) no SSD - easy; buy your own and clone the HDD and you're still alot cheaper than the Dell with your own preferred brand and size of SSD. 2) The rubbish 1366x786 TN panel on the Acer. This is much trickier I prefer lower resolutions for games anyway but 1650x800 or 1080p would be much better for work. Only question is, can you buy and fit a better panel yourself cheaply if you're willing and able?