Manual: criticalstat-bpfcc

criticalstat(8)					   System Manager's Manual				     criticalstat(8)

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 following kernel configurations based on which kernel version you use.
	   - CONFIG_DEBUG_PREEMPT
	   - CONFIG_PREEMPT_TRACER

	   For kernel 4.19 and later:
	   - CONFIG_PREEMPTIRQ_TRACEPOINTS
	   - CONFIG_TRACE_IRQFLAGS
	   - CONFIG_TRACE_PREEMPT_TOGGLE

	   For kernel 4.15 to 4.18:
	   - CONFIG_PREEMPTIRQ_EVENTS
	   - CONFIG_PROVE_LOCKING
	   - CONFIG_DEBUG_PREEMPT Additionally, the following options should be turned off on older kernels:
	   - 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.

USER COMMANDS						 2018-06-07					     criticalstat(8)