Hi Guys, I'm posting on this list after a very long time...so plz excuse me if my question is OT. I had some doubts on how threads are scheduled in 2.6 kernels. A little background of my "issue" first. We're working in an MIPS based embedded system, running a fairly old Linux 2.6.22 kernel (with vendor provided BSP). We write UI applications on top of this system using QT. One of the applications is a photo-viewer like app which fetches image data from the n/w and displays them on the screen in a grid-like manner. The app shows images in a "paged" manner so going from one page to another requires animating the grid with a new set of images. Now the task of decoding the incoming image data is very CPU intensive and so is the animation part. So we used to see the animation suffer when images (for next page were being decoded). So we though of offloading the decoding part to a low priority thread. The main thread mostly used to do 2 main operations - animation (CPU intensive) and n/w i/o (blocking IO). The decoder thread was given the lowest priority and the main GUI thread was given the highest priority (this is QT thread priority and not pthread priority, but QT internally maps such priorities to OS specific values) This helped improve the animation, but 2 implementations that we tried were giving very different and unexpected results: 1. In our first implementation the decoder thread was always running, i.e it was busy-looping even when there was no data to work on. BUT, we were observing that it was getting a chance to run _only_ when the main thread was idle! So it almost looked like once the main thread finished animating (a CPU intensive task) the other thread was getting a chance to run and we used to see all the enqueued images decoded in a "batch". In this implementation the animation was completely smooth as no decoding operation was hampering it. 2. In our 2nd implementation, since busy looping was not a good idea, we changed the decoder thread to sleep (blocking on a mutex) when there was no job to be done. Surprisingly, in this implementation the animation was suffering again. We could see the decoder thread run in-between the main thread's run (which was animating the UI) which could possibly explain the poor animation performance. So my questions: - In the second implementation, why was the low-priority thread running in-between and while doing a busy-loop caused it ran only when the main thread was idle? One of my colleague suggested that since busy-looping is CPU bound, the kernel might be giving it a "nice" value penalty causing it priority to change dynamically. - Is there still a concept of fixed process timeslices for scheduling of processes? - How can I find out if the kernel supports NPTL (kernel managed threads) or plain old linux threads (user-space managed threads)? I was trying to find out more info about the threads when the app is running (using "ps" etc), but it seems that the most useful options are not available in the busybox ver that I'm using. Any other way to get more thread related info about a running application? And again, sorry if this is OT. Thanks, -mandeep _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
