I've been using Ubuntu on my Dell XPS M1330 laptop for almost four years now. I've never had this happen until I upgraded to 12.04 Precise.
What's happening is that the GPU is overheating, causing the BIOS to throttle down the CPU for several minutes at a time. This typically happens when watching YouTube videos in Firefox with Flash, but I've noticed it even happens when watching downloaded YouTube videos in VLC, and it can also happen when doing sustained CPU-intensive activities, like building the kernel.
The reason I'm posting this here is because when this happens, the system fan is not running at high speed. If the fan would speed up properly, it wouldn't overheat. But instead, the fan remains at low speed and the CPU gets gradually throttled down to 800 MHz for several minutes.
I am almost sure that this is a bug in the NVIDIA drivers because:
1. When this laptop was new, an issue arose regarding the 8400M GS chipset's thermal packaging, causing shorter lifetimes; systems were failing left and right. So Dell released a BIOS update that greatly reduced the low temperature threshold for turning off the fan, causing the fan to run more of the time and at higher speeds. However, the BIOS update caused wildly erratic fan behavior until NVIDIA released a driver update. It's clear that the NVIDIA driver does have some control over the fan.
2. In all these years I've never, ever had my laptop overheat, and I'd often hear the fan run at top speed. However, since upgrading to 12.04 Precise, the fan very rarely runs at top speed--especially not when it should be, right before it overheats--and I can regularly cause the overheating and throttling by simply watching a YouTube video. The behavior started occuring right after upgrading.
Because of this bug
, I am not running the NVIDIA driver which ships with Precise, nor the later versions--I'm currently on 290.20, which is the latest driver I found that doesn't freeze X completely from time to time. It seems that Oneiric ships with 280.13, so perhaps a regression was introduced sometime after that version.
I'm not aware of any other software that could interact with the NVIDIA driver and affect the fan speed, so I am guessing it's the driver itself that is the problem. Again, this never, ever happened in four years until I upgraded to Precise, and now it suddenly happens consistently.
I'd be grateful for any help. NVIDIA's drivers have always been great--I've been using them on Linux for almost ten years. But lately I have experienced a few serious regressions. Are there some quality control issues going on?