Matt Mackall wrote: > On Wed, Jun 06, 2007 at 10:28:28AM -0700, Andrew Morton wrote: >> On Wed, 06 Jun 2007 09:12:04 -0400 Mark Hounschell <[EMAIL PROTECTED]> 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. >
>From an earlier thread member: >> Mark writes: >> Again I don't understand why flush_scheduled_work() running on behalf >> of a process affinitized to processor-1 requires cooperation from >> events/2 (affinitized to processor-2) >> when there is an events/1 already affinitized to processor 1? >Oleg write: >flush_workqueue() blocks until any scheduled work on any CPU has run to >completion. If we have some work_struct pending on CPU 2, it can be >completed only when events/2 executes it. Could not flush_scheduled_work() just follow the affinity mask of the task that caused the call to begin with. If calling task had a cpu-mask of 3 then flush_scheduled_work() would do the events/0 and events/1 thing and if the calling task had an affinity mask of 1 then only events/0 would be done? In other words changing what Oleg says above just slightly: flush_workqueue() blocks until any scheduled work on any CPU in the calling tasks affinity mask has run to completion? Thanks Mark - 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/