[arch-general] most efficient way to get linux kernel statistics

[Andre Schmidt]

On Mon, 7 Mar 2016 21:20:18 +0100
Damjan Georgievski <gdamjan at gmail.com> wrote:

> >>> The free command gets its information from /proc/meminfo.
> >>> Performance-wise, it doesn't really matter if a few additional lines
> >>> need to be parsed.  
> >>
> >> Hello,
> >> Thank you Florian. Actually, I already knew it's the same, I just
> >> thought that he could use the free command instead of parsing it
> >> himself. You're right. Performance-wise, it's pretty much the same.
> >>  
> >
> > Sorry, I didn't express myself properly. I didn't mean to criticize
> > free. What I meant to say was that the time it takes to parse
> > /proc/meminfo or free is negligible. It doesn't need to be any more
> > efficient. free parses /proc/meminfo. libgtop parses /proc/meminfo.
> > Querying the information probably takes much more time than parsing it.
> >
> > Your suggestion to use free may indeed be useful if the original poster
> > wants parsing to be slightly simpler and does not mind the additional
> > dependency. My impression was that they considered parsing to be too
> > inefficient.  
> 
> there's also `sysinfo(2)`

ah, thank you!

and now that i found (or rather, thought about it) the source for /proc/meminfo [0] i can see that it uses sysinfo too. but sadly the cached size is not in sysinfo.

then i tried to do what /proc/stat [1] does and after googling learned some facts:

- you can't use "kernel-space" functions in "user-space" apps
  - so i cant use all the same functions as /proc/stat uses
- you can't create new "syscall" functions in a kernel module
  - so i can't "export/map" those "kernel-space" functions to be used in my "user-space" app

so it seems the only way to get deeper than /proc/stat would be to add new "syscalls" to the linux kernel? (for functions like for_each_possible_cpu and kcpustat_cpu)

i'm just a webmonkey, so ill stick to /proc for now :D
(i cant notice my daemon in cpu usage yet, so not really a "problem")

Cheers
Andre Schmidt

[0] https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/fs/proc/meminfo.c
[1] https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/fs/proc/stat.c