Linux VFS cache hit rate script

[William Cohen]

On 04/20/2011 03:04 PM, Jake Maul wrote:
> Greetings all,

Hi Jake,

Thanks for taking the time to submit the example.

> 
> I have recently put a script up on the War Stories page, and it was
> requested of me to also post it to the list, along with a .meta file.
> They're both attached.
> 
> http://sourceware.org/systemtap/wiki/WSCacheHitRate

Why the need for  -DMAXMAPENTRIES=100000 on the second example on the wiki page? There doesn't seem to be any arrays in the script.

> 
> Let me know what you think! It's my first SystemTap script, so I'm
> sure there are improvements that could be made. I'm by no means a
> kernel hacker, or even a C dev... just a lowly sysadmin. :)

Include a short header like the following at the beginning of the script:

#!/usr/bin/env stap
# cache-hit.stp
# Copyright (C) 2011 xxx <xxx@yyy.zzz>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 2 as
# published by the Free Software Foundation.


Should avoid long line lengths in the printf statements. Wrapped lines don't look good in manuals.


The following line sounds unsure, need to check that that is really the case:

 if (devname=="N/A") { /* N/A means cache hit... right? */

It would be good to have a better explanation for the "N/A" check.

-Will