Hi! We're currently evaluating whether PREEMPT_RT will work for a certain use case combining realtime and performance requirements running on a lot of CPUs and using a bunch of RAM. For first tests, we're running a "small" AMD64 test system with 2x2 cores (2 CPUs with 2 cores each) with 8 GB of RAM. We wrote a small testcase which basically has one SCHED_FIFO "realtime" thread which does nothing but sleeping and checking if it wakes up at the right time. In addition, it spawns 20 low-prio "load threads" introducing a lot of malloc/memory access/free load on some GB of RAM. We can see, that the realtime requirements are fulfilled quite well (if using the current glibc with private futexes, but that's another story). The "rt thread" reacts within the expected timeframe with 2.6.22.1-rt9 as well as with 2.6.23-rt1. However, what causes problems is the load balancing of the 20 threads over the available CPU cores: - With 2.6.22.1-vanilla, the threads are distributed over all four available cores - With 2.6.22.1-rt9 (patched, but PREEMPT_RT & friends *disabled*), the threads are distributed *only over two cores*, the others are idling - With 2.6.22.1-rt9 (PREEMPT_RT & friends enabled), the threads are distributed *only over two cores*, the others are idling - With 2.6.23-rt1 (patched, but PREEMPT_RT & friends *disabled*), the threads are distributed over all four cores - With 2.6.23-rt1 (PREEMPT_RT & friends enabled), the threads are distributed *only over two cores*, the others are idling We have not set any CPU affinities in any case. With the 2.6.22 series, I played a bit with patch-2.6.22.1-rt9-broken-out.tar.bz2 and am quite sure that the behaviour change is introduced by preempt-softirqs-core.patch. If I apply anything up to and including this patch (according to the series file), I see that only two cores are used. If I just remove this sole patch, all four cores are used again. Any ideas what causes these issues? Is this somehow connected to NUMA optimizations or just a bug? Known one? Any idea or suggestions welcome... TIA! ---- With kind regards, Gernot Hillier Siemens AG, CT SE 2 Corporate Competence Center Embedded Linux - To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
