lkml.org 
[lkml]   [2005]   [May]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Scheduler: Spinning until tasks are STOPPED
Yuly Finkelberg wrote:
>
>
>
> Hi,
>
> I sent a message regarding this issue earlier, but after re-reading
> it, I realized that it wasn't very clear. Hopefully, this will
> clarify things a little bit:
>
> I have a strange scheduling issue: a bunch of worker tasks are all waiting
> on a wait queue. Each task is woken up by the preceeding, does some work,
> wakes up the next one, and then sends a SIGSTOP to itself. The last task however
> does not stop itself, but instead yield()s until all tasks have reached state
> TASK_STOPPED.
>
> The code looks like this (irrelevant parts cut out):
> ...
> ret = wait_event_interruptible(waitq, next_in_line == myself);
> ...
> (some work)
> ...
> next_in_line = next;
> ret = wakeup_next_one();
> if (!last_one)
> send_sig(SIGSTOP, current, 1);
> else
> spin_until_all_stopped()
>
> When run with 50 tasks, normally this works well. However sometimes one of the
> tasks (never the last one) gets stuck between calling wakeup_next_one() and
> between sending the signal. It accumulates system time, and its stack looks
> like (no pending signals, ti_flags is clear):
>
> c55e7ad0 00000086 c55e6000 c55e7a94 00000046 c55e6000 c55e7ad0 c0109c2d
> 00000000 c0497800 00000001 d38da344 0013bc9c c5632840 00071931 d3d93161
> 0013bc9c c55d546c c05d3960 0000270f c05d3960 c55e6000 c0106f25 c05d3960
>
> Call Trace:
> [<c0106f25>] need_resched+0x27/0x32
>
> (yes, this is not a mistake: this is ALL the stack reported by show_stack())
>
> Normally the spinning task will magically get released after "a while", where
> few seconds < "a while" < 10 minutes and sometimes even longer.
> So the mystery is -
> 1. Why does the task spin for so long ?
> 2. Where does it spin ? (the kernel stack doesn't hint on anything...)
> 3. How can I find out #2 ?
> 4. How to fix it ?
> 5. Is there a better way to make sure a specific task is STOPPED ?
>
> Currently running 2.6.8.1 and 2.6.9 (UP, PREEMPT). I'd appreciate any
> help here...

You're doing this in the *kernel*? It sounds like it should be done
in userspace or done a different way (ie. not with 50 tasks).

And using signals and spinning on yield for synchronisation and
process control in the kernel like this is fairly crazy.

Can't you use a semaphore or something?


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-05-07 09:15    [W:0.071 / U:0.796 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site