aDriv4 - MANAGER

Edit File: biolatency_example.txt

Demonstrations of biolatency, the Linux BPF/bpftrace version. This traces block I/O, and shows latency as a power-of-2 histogram. For example: # ./biolatency-kp.bt Attaching 3 probes... Tracing block device I/O... Hit Ctrl-C to end. ^C @usecs: [256, 512) 2 | | [512, 1K) 10 |@ | [1K, 2K) 426 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| [2K, 4K) 230 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@ | [4K, 8K) 9 |@ | [8K, 16K) 128 |@@@@@@@@@@@@@@@ | [16K, 32K) 68 |@@@@@@@@ | [32K, 64K) 0 | | [64K, 128K) 0 | | [128K, 256K) 10 |@ | While tracing, this shows that 426 block I/O had a latency of between 1K and 2K usecs (1024 and 2048 microseconds), which is between 1 and 2 milliseconds. There are also two modes visible, one between 1 and 2 milliseconds, and another between 8 and 16 milliseconds: this sounds like cache hits and cache misses. There were also 10 I/O with latency 128 to 256 ms: outliers. Other tools and instrumentation, like biosnoop.bt, can shed more light on those outliers. There is another version of this tool in bcc: https://github.com/iovisor/bcc The bcc version provides options to customize the output. "biolatency.bt" is an updated version of "biolatency-kp.bt" and does basically the same thing utilizing the tracepoints instead of kprobes.