On Mon, Oct 18, 2004 at 04:30:54PM -0500, Zajac Adam-AAZ004 wrote: > I'm seeking any help on tuning the Linux kernel running in an embedded > environment to meet some of the soft real-time requirements that we have for > our platform. > Our custom board is based on PPC MPC8540 processor and it runs kernel 2.4.20 > with the low-latency patch and kernel preemption enabled. The applications > running on that board keep experiencing a "task starvation" scenario, which > leads to missing soft real-time deadline requirements. > > We've tried to prioritize the applications that needed to meet these soft > real-time deadlines above other "background" tasks performing unarchiving > operations (gzip + tar) through the means of adjusting dynamic as well as > static priorities. Dynamic priorities were assigned through "nice()" > function and static priorities were assigned for the round robin policy of > the scheduler through "sched_setscheduler()". We've pretty much exhausted > all combinations of the priority assignments without finding the right > configuration that would satisfy both soft real-time deadlines and overall > system performance requirements. > Soft real-time deadlines are being missed during unarchiving procedures. > > Any hints and ideas would be greatly appreciated.
Could you elaborate a little on what those soft-realtime requirements are? Are they sub-millisecond, milliseconds ...? FWIW, I use 2.4.21 kernel + preempt patch (MV one, _NOT_ from rml patches), low-lat, O(1) scheduler and HZ = 1000. Thread with real-time priority (any, all other threads run with SCHED_OTHER) and FIFO scheduler doing 10ms sleep runs pretty robust on 440 hardware. During worst case scenario - heavy disk (SCSI) activity, I'm seeing rare sleeps up to 18-20ms. -- Eugene
