On Sat, 07 Apr 2007 16:31:39 +0900 Satoru Takeuchi <[EMAIL PROTECTED]> wrote:
> When I was examining the following program ... > > 1. There are a large amount of small jobs takes several msecs, > and the number of job increases constantly. > 2. The process creates a thread or a process per job (I examined both > the thread model and the process model). > 3. Each child process/thread does the assigned job and exit immediately. > > ... I found that the thread model's latency is longer than proess > model's one against my expectation. It's because of the current > sched_fork()/sched_exit() implementation as follows: > > a) On sched_fork, the creator share its timeslice with new process. > b) On sched_exit, if the exiting process didn't exhaust its first > timeslice yet, it gives its timeslice to the parent. > > It has no problem on the process model since the creator is the parent. > However, on the thread model, the creator is not the parent, it is same > as the creator's parent. Hence, on this kind of program, the creator > can't retrieve shared timeslice and exausts its timeslice at a rate of > knots. In addition, somehow, the parent (typically shell?) gets extra > timeslice. > > I believe it's a bug and the exiting process should give its timeslice > to the creator. Now I have some patch plan to fix this problem as follow: > > a) Add the field for the creator to task_struct. It needs extra memory. > b) Doesn't add extra field and have thread's parent the creater, which is > same as process creation. However it has many side effects, for example, > we also need to change sys_getppid() implementation. > > What do you think? Any comments are welcome. This comes at an awkward time, because we might well merge the staircase/deadline work into 2.6.22, and I think it rewrites the part of the scheduler which is causing the problems you're observing. Has anyone verified that SD fixes this problem and the one at http://lkml.org/lkml/2007/4/7/21 ? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
