Messages in this thread | | | Date | Wed, 6 Jun 2007 20:31:28 -0500 | From | Matt Mackall <> | Subject | Re: floppy.c soft lockup |
| |
On Wed, Jun 06, 2007 at 10:28:28AM -0700, Andrew Morton wrote: > 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.
The usual alternative is to manually chrt the relevant kernel threads to RT priority and adjust the priority scheme of their processes appropriately.
-- Mathematics is the supreme nostalgia of our time. - 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/
| |