[systemd-devel] systemd-udevd: excessive I/O usage

[Peeters Simon]

2012/6/4 Kok, Auke-jan H <auke-jan.h.kok at intel.com>:
> On Mon, Jun 4, 2012 at 1:14 PM, Peeters Simon <peeters.simon at gmail.com> wrote:
>> 2012/6/4 Kok, Auke-jan H <auke-jan.h.kok at intel.com>:
>>> On Mon, Jun 4, 2012 at 12:49 PM, Peeters Simon <peeters.simon at gmail.com> wrote:
>>>> Hello all.
>>>>
>>>> while trying to optimize my bootup i noted that i could not squeeze it
>>>> under 17seconds userspace
>>>>
>>>> Looking at the bootchart revealed that this is mainly due to
>>>> systemd-udevd consuming 60% of my bootup I/O.
>>>> This means i lose 12 seconds of bootup just to one process.
>>>
>>> can you post the bootchart SVG file?
>>>
>>> I'm assuming you're using this version of bootchart:
>>>
>>> http://foo-projects.org/~sofar/bootchart/bootchart-1.18.tar.gz
>> apparently not, i did just yum install bootchart and it reports to be
>> version 0.14, will take a look at this version.
>>>
>>>> i was wondering whether there is any way to get this more optimized?
>>>> fewer udev rules? more readahead? something else? (i have no idea what
>>>> this I/O is, except for the fact that it is scattered all over the
>>>> place)
>>>>
>>>> this was with systemd 184(from fedora18) on fedora 17.
>>>
>>> The bootchart SVG will tell us most of the stuff that want to know -
>>> so please share it.
>> here you are (this is with fedoras default bootchart, will try the
>> other one later.)
>
> the old version obscures a lot of information - in this case all the IO
> gets attributed to udev while in fact it's probably one of your kernel
> threads. The version of bootchart I maintain should provide a much
> clearer picture of where the bottlenecks are.

well, here it is, it does not really show the I/O activity the old one
shows (it seems like this one only shows throughput)

between 9 and 15 seconds almost nothing seems to happen, almost no
cpu, almost no I/O throughput, only the sound of my harddisk seeking
the whole time, could it be because udev spawns so many children that
want access to the disk simultaneously?

simon