Hi Stanislav > Linux nxt 3.12.15-rt25+ #83 PREEMPT RT Thu Apr 17 20:54:00 CEST 2014 > armv5tejl GNU/Linux > > > # tracer: irqsoff > # > # irqsoff latency trace v1.1.5 on 3.12.15-rt25+ > # -------------------------------------------------------------------- > # latency: 2224 us, #6/6, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0) > # ----------------- > # | task: swapper-0 (uid:0 nice:0 policy:0 rt_prio:0) > # ----------------- > # => started at: rcu_idle_enter > # => ended at: arch_cpu_idle > # > # > # _--------=> CPU# > # / _-------=> irqs-off > # | / _------=> need-resched > # || / _-----=> need-resched_lazy > # ||| / _----=> hardirq/softirq > # |||| / _---=> preempt-depth > # ||||| / _--=> preempt-lazy-depth > # |||||| / _-=> migrate-disable > # ||||||| / delay > # cmd pid |||||||| time | caller > # \ / |||||||| \ | / > <idle>-0 0d...1.. 2us+: rcu_idle_enter > <idle>-0 0d...2.. 11us+: T.796 <-rcu_idle_enter > <idle>-0 0d...2.. 17us!: arch_cpu_idle <-cpu_startup_entry > <idle>-0 0d...1.. 2219us+: arch_cpu_idle > <idle>-0 0d...1.. 2234us+: trace_hardirqs_on <-arch_cpu_idle > <idle>-0 0d...1.. 2303us : <stack trace> > => arch_cpu_idle > => cpu_startup_entry > => start_kernel > > Why are interrupts disabled here (and are they really disabled)? > > $ egrep "IDLE|SMP|HZ" .config > CONFIG_BROKEN_ON_SMP=y > CONFIG_HZ_PERIODIC=y > # CONFIG_NO_HZ_IDLE is not set > # CONFIG_NO_HZ is not set > CONFIG_GENERIC_SMP_IDLE_THREAD=y > CONFIG_GENERIC_IDLE_POLL_SETUP=y > CONFIG_HZ_FIXED=0 > # CONFIG_HZ_100 is not set > # CONFIG_HZ_200 is not set > CONFIG_HZ_250=y > # CONFIG_HZ_300 is not set > # CONFIG_HZ_500 is not set > # CONFIG_HZ_1000 is not set > CONFIG_HZ=250 > # CONFIG_CPU_IDLE is not set > # CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED is not set > > Configuring > CONFIG_CPU_IDLE=y > CONFIG_CPU_IDLE_GOV_LADDER=y > does not help > > Maybe it is just some tracing infrastructure interference - the effect > of enabling the tracing is huge on this platform for some reason. > Just enabling the irqsoff tracing makes the machine unsuitable > for any serious load. Are you sure that this is not the cpu idle latency? I patched out the idle mechanism on i.mx35 since waking up took much to long for RT usage. The CPU is running a little hotter then, but after all the thermal envelop always has to to cope with maximum load, so i guess this should do no harm besides more energy churn. Best regards Tim -- 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
