Bug#670797: linux-image-3.2.0-2-686-pae: CPU load not being distributed
On Sun, Apr 29, 2012 at 01:44:56PM -0300, Wido wrote:
> I tend to follow new kernel feature from 'the H online' and I don't recall
> seeing something like this was ever mentioned. I know current default sched
> is the BFS, but it doesn't mention such behavior.
The scheduler is CFS. BFS is someone else's project outside of
mainline Linux.
> A little test I did was opening a youtube video (I use chrome), the cpu was
> almost 100% but, in htop. around 70% was show as low pri. If I run another
> program, lets say VirtualBox, they start to share the same core, instead of
> using another one that is free.
That does sound wrong. However it is possible that the CPU frequency
is being changed so that that single core still has enough cycles to
run both programs without slowing them down.
> This behavior seems buggy to me. I've been using Debian since Woody, this
> desktop has almost 1 and a half year, and this started to happen when I
> installed 3.1
Here's how you can test this:
1. Start the video playing
2. Measure how long it takes to boot a particular VM in VirtualBox
3. Repeat this another 4 times, so you have a total of 5 runs
4. Use taskset to force the video player and VirtualBox onto separate
cores
5. Repeat another 5 times
By comparing the two sets of 5 times, we can see whether the scheduler
should be using more than one core. (Also, if the video plays more
smoothly in step 5, then the scheduler should be using two cores.
But this is not as easy to measure objectively.)
You can substitute whatever else you're interested in for steps 1 and
2, just as long as it is something repeatable.
Ben.
--
Ben Hutchings
We get into the habit of living before acquiring the habit of thinking.
- Albert Camus
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