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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CeriseCogburn - Sunday, July 29, 2012 - link
Looks like the truth is less than half on not so old macshttp://www.ebay.com/itm/Mac-Book-Pro-17-2-3Ghz-i7-...
BillatDell - Wednesday, July 25, 2012 - link
Very fair review, all things considered, Jarred. Thank you very much. I am the Dell employee you linked to out on Notebook Review Forums.I am wondering if skin temps matter to you and the Anandtech audience. I'd be curious to see a skin temp comparison under similar loads between the XPS and any competitive system, particularly the rMBP and MBP. It may not have any impact on anyone's buying decision if they don't see the numbers, but it may or may not matter to others if there turns out to be a wide disparity. Hard to tell if the cost/benefit analysis of our having a hard set skin temp spec across the board for all platforms stands to reason, given pretty much universal approval of how the MBP performs and the obvious lack of popularity with our current thermal/throttling scheme.
Anyone else have any thoughts on skin temps, or is it a non-factor? I'm interested to hear and get some thoughts out here on the record.
Great community. Great site. Thanks for all you do.
yyrkoon - Wednesday, July 25, 2012 - link
If I understand what you mean by "skin-temps" Bill. No for me personally it does not matter. The laptops I use currently serve as desktop replacements. As we are completely off-grid using solar, wind, and sometimes generators.However, I would admit. That we are not the norm for most users.
My own personal concerns are getting what I paid for but, stability first. Just for example. I like to play a lot of games, but have many computer related hobbies. So gaming performance for me tends to be my own benchmark. Of course I also have a price range I tend to stick within.
Unfortunately for me, and Dell. The XPS series is generally out of my own price range. However that could change. With that said, I have been keeping an eye on your companies products. Specifically the XPS mobile line.
JarredWalton - Wednesday, July 25, 2012 - link
Hi Bill, glad to have you on here. Skin (surface) temperatures are something I used to report, but them my thermometer broke and we added a couple more laptop reviewers and I figured I would just forget it and use internal temperatures. What I'd REALLY love to get is one of those digital thermal imaging cameras, but sadly they're a bit too much for me to convince Anand to buy a couple.As for what I think of skin temps, there's a balance that needs to be maintained, and certain areas can get hotter without bothering the user as much. If we're looking at a desktop replacement, it's not too big a concern, but for the more portable systems I definitely feel it's important. Ideally, I want the palm rest, keyboard, and the bottom "thigh" areas to be cooler, while the rear of the laptop (e.g. where the vent is on the XPS 15) can be hotter. 35C or less is generally what I'd like, but I live in WA so temperatures aren't as hot as, say, AZ or CA. If I were living in a hotter climate, I'd probably want even cooler running laptops.
Anyway, as you can probably glean from the review, I'd say you need stability as well as the ability to hit the rated performance on all parts. For the CPU, that means CPU clocks of 2.1GHz or higher regardless of workload should be possible pretty much indefinitely--and certainly if you're in a 75F or cooler environment. If the heatsink/fan can't keep the CPU and GPU at acceptable temperatures under load, then the hardware has been over-specced for the cooling. (We saw this exact same issue on Acer's TimelineX 3830TG, incidentally. Thin and light with reasonably fast hardware, but with gaming workloads the CPU would drop to 1.2GHz.)
My one thought that I keep coming back to on the XPS 15 is that it simply needs a higher RPM fan. Maybe the BIOS can kick the fan speed up one more level, but right now it just doesn't seem capable of cooling effectively at the current maximum RPM. A more drastic change would involve looking at the exhaust and trying to make that "breath" easier, as right now the bottom of the LCD/hinge seems to restrict airflow. Would either of these items be enough to fix the throttling problem? I don't know, but I am very surprised that this wasn't caught and addressed before retail units were shipping to the public.
Here's hoping we'll get a reasonable firmware fix in the near future!
Voldenuit - Wednesday, July 25, 2012 - link
OK, off the bat, I want to apologize for sounding like a broken record.But I was vocally unhappy with the Acer sporting a TN panel at $1400, and I'm even more unhappy with the Dell doing the same thing at $1700. What makes manufacturers think they could (or should) get away with foisting this sort of crap on people?
Next time I should just skip to the LCD page before reading any further. :/
Grok42 - Wednesday, July 25, 2012 - link
I agree. My preference of OS in order is Linux, Windows, BeOS, OS X. I also hate laptops as they are typically slower, hotter and cost more than a desktop. That said, as of today my next computer will probably be a rMBP because of the screen. My profession is computers and ~$1000 is nothing compared to what I will gain with a better tool with which to do my work. The PC industry better wake up and start offering multiple 4k displays or they are going to be wiped out.Doomtomb - Wednesday, July 25, 2012 - link
I like Dell and I want to see them succeed in the consumer/enterprise PC market. However, this review of the new 2012 Dell XPS 15 reminds me of the same niggles I had with my Studio XPS 16 purchased in early 2010. The one area that my Studio XPS 16 will always dominate is display (RGB-LED 1080p) displays colors perfectly unlike the XPS 15. Both of these computers are very premium products with price tags to match. The problems with the Studio XPS 16 were build quality (lousy hinges, seems between aluminum parts), heavy, battery life, and heat. It tries to push the boundaries between size, style, build quality, and performance but you can't have it all. It ended up being too big and heavy and just not quite as powerful as my friend's Alienwares. The battery life was also sub-par for class. I'd just rather recommend getting a thin and light, a gaming desktop replacement, or a MacBook with Retina Display.antef - Wednesday, July 25, 2012 - link
After the ridiculous overheating and throttling (to the point of an unusable machine) I've experienced with my Dell Precision, and reading this article with similar concerns, I can't imagine I'll be trusting a Dell for any high-performance workloads anytime soon.Death666Angel - Wednesday, July 25, 2012 - link
I was going to comment on how the MBP 15" gets mentioned in nearly every paragraph without being in the charts. Then I thought: "Well, they do have the Bench for those things." So I went there trying to compare this with the MBP 15" 2012. But you don't have the Dell there (yet) and you have no Apple 15" of any sort in there. How come? :-)tipoo - Wednesday, July 25, 2012 - link
Indeed, I'd like some macs on there