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I can capture > Kernel and UST events. > > My purpose is to investigate why a periodic task, running on an > isolated core, has occasional blips i.e. it's period (duration) > extends. > > I have inserted tracepoints to mark normal and extended durations. In > Trace Compass the blip tracepoint is preceded by a brown state that is > 'SOFT IRQ 1'. This extends down all cores. It lasts 105us and is > likely to be the reason for the blip. > > Please could someone explain to me what may be happening here and how > can I find out the reason for this SOFT IRQ? See include/linux/interrupt.h from the Linux kernel: enum { HI_SOFTIRQ=0, TIMER_SOFTIRQ, NET_TX_SOFTIRQ, NET_RX_SOFTIRQ, BLOCK_SOFTIRQ, IRQ_POLL_SOFTIRQ, TASKLET_SOFTIRQ, SCHED_SOFTIRQ, HRTIMER_SOFTIRQ, RCU_SOFTIRQ, /* Preferable RCU should always be the last softirq */ NR_SOFTIRQS }; So SOFT IRQ 1 would be TIMER_SOFTIRQ. Note that we have a TODO in lttng-modules: lttng_dump_softirq_vec() Implementing this by dumping this softirq table mapping numbers to names would be a welcome contribution. Thanks, Mathieu > > Best regards > David -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com