[gentoo-user] Re: How to find out to what file(...) writes goes on a idle system...

[James]

<meino.cramer <at> gmx.de> writes:


> > (1) Then pursue quantifying with tools just what is causing the
> > writes, strategies for minimization and monitoring as needed.

> > So folks are going down path (1) with you, that is fine.

Prong (1) includes all issues related to systemd. Probably embedded
experience with systemd is rare, just guessing. Certainly I have none
of that experience. So post to those iotop responses and remind
folks you are using systemd on an embedded (gentoo) micro.

root  563  1  0 15:37 ?   00:00:00 /lib/systemd/systemd-udevd --daemon




> > (2) First minimize those write to your non-mechanical memory.

> > I have dozens of tricks to minimize a gentoo system. But it is quite
> > a bit of work, just so you know. It's not a do this and it great. It
> > more like, try this, study the result and then alter the strategy.
> >
> > hth,
> > James
> >
>
> Hi,
>
> thank you very for all help I received regarding my question.
>
> The system is already down to a limit. The by default running
> processes are:
>
> root         1     0  0 15:36 ?        00:00:00 init [3]
> root         2     0  0 15:36 ?        00:00:00 [kthreadd]
> root         3     2  0 15:36 ?        00:00:01 [ksoftirqd/0]
> root         5     2  0 15:36 ?        00:00:00 [kworker/0:0H]
> root         7     2  0 15:36 ?        00:00:00 [khelper]
> root         8     2  0 15:36 ?        00:00:00 [kdevtmpfs]
> root       160     2  0 15:36 ?        00:00:00 [writeback]
> root       162     2  0 15:36 ?        00:00:00 [crypto]
> root       164     2  0 15:36 ?        00:00:00 [bioset]
> root       166     2  0 15:36 ?        00:00:00 [kblockd]
> root       168     2  0 15:36 ?        00:00:00 [cfg80211]
> root       169     2  0 15:36 ?        00:00:00 [kworker/0:1]
> root       280     2  0 15:36 ?        00:00:00 [kswapd0]
> root       296     2  0 15:36 ?        00:00:00 [fsnotify_mark]
> root       372     2  0 15:36 ?        00:00:00 [ipv6_addrconf]
> root       398     2  0 15:36 ?        00:00:00 [deferwq]
> root       406     2  0 15:36 ?        00:00:12 [mmcqd/0]
> root       412     2  0 15:36 ?        00:00:00 [kworker/0:2]
> root       415     2  0 15:36 ?        00:00:00 [jbd2/mmcblk0p2-]
> root       416     2  0 15:36 ?        00:00:00 [ext4-rsv-conver]
> root       563     1  0 15:37 ?        00:00:00 /lib/systemd/systemd-udevd
--daemon
> root       952     1  0 15:37 ?        00:00:00 /usr/sbin/ifplugd --iface=usb0
> root      1380     1  0 15:37 ?        00:00:00 /usr/sbin/sshd
> root      1399     1  0 15:37 tty1     00:00:00 /sbin/agetty 38400 tty1 linux
> root      1400     1  0 15:37 tty2     00:00:00 /sbin/agetty 38400 tty2 linux
> root      1401     1  0 15:37 tty3     00:00:00 /sbin/agetty 38400 tty3 linux
> root      1402     1  0 15:37 tty4     00:00:00 /sbin/agetty 38400 tty4 linux
> root      1403     1  0 15:37 tty5     00:00:00 /sbin/agetty 38400 tty5 linux
> root      1404     1  0 15:37 tty6     00:00:00 /sbin/agetty 38400 tty6 linux
> root      1405     1  0 15:37 ttyS0    00:00:00 /sbin/agetty -L 9600 ttyS0
vt100
> root      1406  1380  0 15:37 ?        00:00:02 sshd: root <at> pts/0
> root      1412  1406  0 15:37 pts/0    00:00:00 screen -R -d
> root      1414  1412  0 15:37 ?        00:00:01 SCREEN -R -d
> root      1415  1414  0 15:37 pts/1    00:00:05 -/bin/zsh
> root      1434     2  0 15:38 ?        00:00:00 [kworker/0:1H]
> root      1866     2  0 15:43 ?        00:00:00 [kworker/u2:0]
> root      8556     2  0 16:49 ?        00:00:00 [kworker/u2:2]

I'd research "kworker"

http://askubuntu.com/questions/33640/kworker-what-is-it-and-why-is-it-hogging-so-much-cpu

 
> The count of getty processes may be decreaseable...but the rest is ok,
> I think.

Those are static and just sitting incase you need a getty, so not a problem

> When I do a ftop I get no process, which have an open file handle for
> writes...sometimes screen writes to utmp but thats it.

With a traditional (non systemd) approach, init scripts just fire
up things at boot time and such. With systemd, I have no idea
what's going on. It's a curious situation and maybe systemd has
no issue in your excessive writes; pure speculation on my part.
But an embedded system just sitting idle should use very little
resource and sit quietly, in my experiences.


> I suspect the swapfile I mounted as swapdevice for being guilty.
> I will deactivate that and we will see then.

good thing to examine.

> When looking at /proc/diskstats: Will I see writes to FIFOs on the
> disk as writes to the disk???
> If YES...it would explain it...


Also good to look at.

I usually use ext2 or one of the newer files systems, just for solid state
memory. Here is a good link to get your research your fs options.

http://free-electrons.com/blog/managing-flash-storage-with-linux/

Since you have (2) boards, have you considered installing the second one
differently (different file system, no systemd  etc etc to compare the
2 results?  If you can put different install-varients on different usb/sd/?
media, then you can just power down and change them out while comparing
resource utilization; just a thought, but something I do routinely.


Also, you need to get a custom/stripped kernel building methodology 
establish so you can try to reduce the kernel size by eliminating things
you do not use, testing scheduler options and a host of things.

Your entire toolchain needs to be documented and keep track of what 
you change and the results of which test you run, when and such.

Also,  when compiling a kernel for a minimize system I find that using
(CFLAGS="-Os""  yields faster and small executables) and is an excellent
way to reduce resource loading on a minimized or embedded system.

It's going to be a long journey, so keep meticulous records of what you
try, the results and your conclusions for the best path forward.


I'm out for a while.
hth,
James