NAME

       criticalstat - A tracer to find and report long atomic critical sections in kernel

SYNOPSIS

       criticalstat [-h] [-p] [-i] [-d DURATION]

DESCRIPTION

       criticalstat traces and reports occurrences of atomic critical sections in the kernel with
       useful stacktraces showing the origin of them. Such critical sections frequently occur due
       to  use of spinlocks, or if interrupts or preemption were explicitly disabled by a driver.
       IRQ routines in Linux are also executed with interrupts disabled. There are many  reasons.
       Such  critical  sections  are  a  source  of  long latency/responsive issues for real-time
       systems.

       This works by probing the preempt/irq and cpuidle tracepoints in the kernel.   Since  this
       uses  BPF,  only the root user can use this tool. Further, the kernel has to be built with
       certain CONFIG options enabled. See below.

REQUIREMENTS

       Enable CONFIG_PREEMPT_TRACER, CONFIG_PREEMPTIRQ_EVENTS  (CONFIG_PREEMPTIRQ_TRACEPOINTS  in
       kernel  4.19  and  later)  and  CONFIG_DEBUG_PREEMPT.  Additionally, the following options
       should be DISABLED on older kernels: CONFIG_PROVE_LOCKING, CONFIG_LOCKDEP.

OPTIONS

       -h     Print usage message.

       -p     Find long sections where preemption was disabled on local CPU.

       -i     Find long sections where interrupt was disabled on local CPU.

       -d DURATION
              Only identify sections that are longer than DURATION in microseconds.

EXAMPLES

       Run with default options: irq disabled for more than 100 uS
              # criticalstat

       Find sections with preemption disabled for more than 100 uS.
              # criticalstat -p

       Find sections with IRQ disabled for more than 500 uS.
              # criticalstat -d 500

       Find sections with preemption disabled for more than 500 uS.
              # criticalstat -p -d 500

OVERHEAD

       This tool can cause overhead if the application is spending a lot of time in kernel  mode.
       The  overhead  is variable but can be 2-4% of performance degradation. If overhead is seen
       to be too  much,  please  pass  a  higher  DURATION  to  the  -d  option  to  filter  more
       aggressively.

SOURCE

       This is from bcc.

              https://github.com/iovisor/bcc

       Also  look  in  the bcc distribution for a companion _examples.txt file containing example
       usage, output, and commentary for this tool.

OS

       Linux

STABILITY

       Unstable - in development.

AUTHOR

       Joel Fernandes

SEE ALSO

       Linux kernel's preemptoff and irqoff tracers.