Messages in this thread | | | Date | Wed, 6 Jun 2007 10:28:28 -0700 | From | Andrew Morton <> | Subject | Re: floppy.c soft lockup |
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On Wed, 06 Jun 2007 09:12:04 -0400 Mark Hounschell <markh@compro.net> wrote:
> > > > As far as a 100% CPU bound task being a valid thing to do, it has been > > done for many years on SMP machines. Any kernel limitation on this > > surely must be considered a bug? > > > > Could someone authoritatively comment on this? Is a SCHED_RR/SCHED_FIFO > 100% Cpu bound process supported in an SMP env on Linux? (vanilla or -rt)
It will kill the kernel, sorry.
The only way in which we can fix that is to allow kernel threads to preempt rt-priority userspace threads. But if we were to do that (to benefit the few) it would cause _all_ people's rt-prio processes to experience glitches due to kernel activity, which we believe to be worse.
So we're between a rock and a hard place here.
If we really did want to solve this then I guess the kernel would need some new code to detect a 100%-busy rt-prio process and to then start premitting preemption of it for kernel thread activity. That detector would need to be smart enough to detect a number of 100%-busy rt-prio processes which are yielding to each other, and one rt-prio process which keeps forking others, etc. It might get tricky. - 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/
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