iovisor/bcc

print_log2_hist to strip leading zeros

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#1,109 opened on Apr 12, 2017

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enhancementhelp wanted

Description

Instead of this:

# ./funclatency vfs_write
Tracing 1 functions for "vfs_write"... Hit Ctrl-C to end.
^C
     nsecs               : count     distribution
         0 -> 1          : 0        |                                        |
         2 -> 3          : 0        |                                        |
         4 -> 7          : 0        |                                        |
         8 -> 15         : 0        |                                        |
        16 -> 31         : 0        |                                        |
        32 -> 63         : 0        |                                        |
        64 -> 127        : 0        |                                        |
       128 -> 255        : 0        |                                        |
       256 -> 511        : 0        |                                        |
       512 -> 1023       : 0        |                                        |
      1024 -> 2047       : 1        |                                        |
      2048 -> 4095       : 400      |*                                       |
      4096 -> 8191       : 4250     |*******************                     |
      8192 -> 16383      : 8652     |****************************************|
     16384 -> 32767      : 4663     |*********************                   |
     32768 -> 65535      : 453      |**                                      |
     65536 -> 131071     : 17       |                                        |
    131072 -> 262143     : 0        |                                        |
    262144 -> 524287     : 0        |                                        |
    524288 -> 1048575    : 0        |                                        |
   1048576 -> 2097151    : 0        |                                        |
   2097152 -> 4194303    : 1        |                                        |
Detaching...

Print this:

# ./funclatency vfs_write
Tracing 1 functions for "vfs_write"... Hit Ctrl-C to end.
^C
     nsecs               : count     distribution
      1024 -> 2047       : 1        |                                        |
      2048 -> 4095       : 400      |*                                       |
      4096 -> 8191       : 4250     |*******************                     |
      8192 -> 16383      : 8652     |****************************************|
     16384 -> 32767      : 4663     |*********************                   |
     32768 -> 65535      : 453      |**                                      |
     65536 -> 131071     : 17       |                                        |
    131072 -> 262143     : 0        |                                        |
    262144 -> 524287     : 0        |                                        |
    524288 -> 1048575    : 0        |                                        |
   1048576 -> 2097151    : 0        |                                        |
   2097152 -> 4194303    : 1        |                                        |
Detaching...

To keep the output more concise. This is especially noticeable by tools that print multiple histograms.

Contributor guide

Tech stack
c
Domain
clideveloper experience
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Familiarity with CBasic understanding of BPF toolsUnderstanding of histogram output
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Locate the function `print log2 hist` in the bcc source code (likely in libbpf tools or similar). Study how it currently iterates over histogram buckets and prints each row. Modify the logic to skip printing rows where the count is zero, except possibly the first and last non zero rows to maintain context. Ensure the output remains correctly aligned. Test with `funclatency` or similar tools to verify the new output matches the example in the issue.
print_log2_hist to strip leading zeros · iovisor/bcc#1109 | Good First Issue