On Sat, 26 Sep 2015, Matthias Meier wrote: > Hi, > > using cyclictest I measure long max latencies of >10ms on a Wandboard dual > (Freescale i.MX6 dual Cortex-A9 SoC). > > The latency problem happens with diffent scenarios: > - without or with rt-patch (4.1.7-rt8 w. CONFIG_PREEMPT_RT_FULL) > - different Kernels (3.17, 4.1, 4.2 w. CONFIG_PREEMPT__LL) > - different CPU governors including 'performance' > - independant of CPU load > - even with no other userspace processes but init, the login sh and cyclictest > (I use a minimal builroot rfs). > - independant of cyclictest prio > > Using the same buildroot rfs on a A20 SoC (bananapro) with 4.1.7-rt8 shows > acceptable rt-latencies of ~ 200us. > > Ftracing 'irqsoff' on the rt-patched 4.1 kernel shows always long latency > after 'raw_spin_lock_irq' (see log below). > > Do you think it is a driver which stalls or hrtimer not working correctly on > this SoC or someting else? > If it is a driver, how could I find out which it is? Try to capture the issue with full function tracing. cyclictest --smp -p80 -m -f -b 5000 That stops the tracer when the latency is > 5ms. You might have to increase the trace buffer size. Please upload the trace to some place or send it to me privately (it's over the size limit of the list). Thanks, tglx -- 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
