bcc-criticalstat(8)

1criticalstat(8)             System Manager's Manual            criticalstat(8)
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NAME

6       criticalstat  -  A  tracer to find and report long atomic critical sec‐
7       tions in kernel
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SYNOPSIS

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

13       criticalstat traces and reports occurrences of atomic critical sections
14       in  the kernel with useful stacktraces showing the origin of them. Such
15       critical sections frequently occur due to use of spinlocks, or  if  in‐
16       terrupts  or  preemption were explicitly disabled by a driver. IRQ rou‐
17       tines in Linux are also executed with interrupts  disabled.  There  are
18       many  reasons.  Such critical sections are a source of long latency/re‐
19       sponsive issues for real-time systems.
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21       This works by probing the preempt/irq and cpuidle  tracepoints  in  the
22       kernel.   Since  this  uses  BPF, only the root user can use this tool.
23       Further, the kernel has to be built with  certain  CONFIG  options  en‐
24       abled. See below.
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REQUIREMENTS

28       Enable  CONFIG_PREEMPT_TRACER, CONFIG_PREEMPTIRQ_EVENTS (CONFIG_PREEMP‐
29       TIRQ_TRACEPOINTS in kernel 4.19 and  later)  and  CONFIG_DEBUG_PREEMPT.
30       Additionally,  the  following  options should be DISABLED on older ker‐
31       nels: CONFIG_PROVE_LOCKING, CONFIG_LOCKDEP.
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OPTIONS

34       -h     Print usage message.
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36       -p     Find long sections where preemption was disabled on local CPU.
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38       -i     Find long sections where interrupt was disabled on local CPU.
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40       -d DURATION
41              Only identify sections that are  longer  than  DURATION  in  mi‐
42              croseconds.
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EXAMPLES

45       Run with default options: irq disabled for more than 100 uS
46              # criticalstat
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48       Find sections with preemption disabled for more than 100 uS.
49              # criticalstat -p
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51       Find sections with IRQ disabled for more than 500 uS.
52              # criticalstat -d 500
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54       Find sections with preemption disabled for more than 500 uS.
55              # criticalstat -p -d 500
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OVERHEAD

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

65       This is from bcc.
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67              https://github.com/iovisor/bcc
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69       Also look in the bcc distribution for a  companion  _examples.txt  file
70       containing example usage, output, and commentary for this tool.
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OS

73       Linux
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STABILITY

76       Unstable - in development.
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AUTHOR

79       Joel Fernandes
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