On Fri, 17 Jan 2020 18:13:31 +0100 Michal Koutný <mkoutny@xxxxxxxx> wrote:
> Hello.
>
> On Thu, Jan 09, 2020 at 11:44:15AM -0800, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > I looked at it - there wasn't really any compelling followup.
> FTR, I noticed udevd consuming non-negligible CPU cycles when doing some
> cgroup stress testing. And even extrapolating to less artificial
> situations, the udev events seem to cause useless tickling of udevd.
>
> I used the simple script below
> cat measure.sh <<EOD
> sample() {
> local n=$(echo|awk "END {print int(40/$1)}")
>
> for i in $(seq $n) ; do
> mkdir /sys/fs/cgroup/memory/grp1 ;
> echo 0 >/sys/fs/cgroup/memory/grp1/cgroup.procs ;
> /usr/bin/sleep $1 ;
> echo 0 >/sys/fs/cgroup/memory/cgroup.procs ;
> rmdir /sys/fs/cgroup/memory/grp1 ;
> done
> }
>
> for d in 0.004 0.008 0.016 0.032 0.064 0.128 0.256 0.5 1 ; do
> echo 0 >/sys/fs/cgroup/cpuacct/system.slice/systemd-udevd.service/cpuacct.usage
> time sample $d 2>&1 | grep real
> echo -n "udev "
> cat /sys/fs/cgroup/cpuacct/system.slice/systemd-udevd.service/cpuacct.usage
> done
> EOD
>
> and I drew the following ballpark conclusion:
> 1.7% CPU time at 1 event/s -> 60 event/s 100% cpu
>
> (The event is one mkdir/migrate/rmdir sequence. Numbers are from dummy
> test VM, so take with a grain of salt.)
Thanks. What effect does this patch have upon these numbers?
>
> > If this change should be pursued then can we please have a formal
> > resend?
> Who's supposed to do that?
Typically the author, but not always. If someone else is particularly
motivated to get a patch merged up they can take it over.
