On Wed, Aug 03, 2016 at 12:48:49PM -0500, Eric W. Biederman wrote: > cool linux <linux.cool.hot@xxxxxxxxx> writes: > > > Hi, > > > > I have executed below script on 3.16 kernel and it took to finish almost > > 1.30sec to 2 minutes, where as in my older kernel(3.2.30) it took only 3 > > secs. > > > > ================================================ > > date > > > > for (( i=1; i <= 2000; i++ )) > > do > > ip netns exec gmk ip link show > /dev/null > > done > > > > date > > ================================================ > > > > Please guide me why this behavior in 3.16 kernel ? > > Good question. What happens on a modern kernel? 4.7 is the most recent > release, 3.16 was released two years ago. My hunch is that you just > started using systemd and it has changed the defaults with all of the > mounts. But shrug. I don't recall how all of those relevant kernel > pieces operated two years ago. Hi, I did a few experiments and saw the same degradation. I used rhel7 and fedoara 23, they both uses systemd. I executed this test on the rhel7 kernel (3.10++). [ ~]# time for (( i=1; i <= 2000; i++ )); do ip netns exec gmk ip link show > /dev/null; done real 0m4.837s user 0m0.983s sys 0m3.885s Then I executed it in Fedora 23 (4.6.4-201.fc23.x86_64) in the same hardware. The result time is much worse. [ ~]# time for i in `seq 2000`; do ip netns exec gmk ip link show; done > /dev/null real 0m36.067s user 0m1.374s sys 0m3.677s Then I tried to exclude a mount namespace: [ ~]# time for i in `seq 2000`; do nsenter --net=/run/netns/gmk ip link show; done > /dev/null real 0m4.476s user 0m1.039s sys 0m3.438s It helps, so the problem is defenetly about mount namespaces. Then I tried to create a clean mount namespace, but this doesn't affect results: [ ~]# cat /proc/self/mountinfo 84 83 253:0 / / rw,relatime - ext4 /dev/mapper/fedora-root rw,seclabel,data=ordered 90 84 0:4 / /proc rw,nosuid,nodev,noexec,relatime - proc proc rw 93 84 0:17 / /sys rw,nosuid,nodev,noexec,relatime - sysfs sysfs rw,seclabel 111 84 0:20 / /run rw,nosuid,nodev - tmpfs tmpfs rw,seclabel,mode=755 [ ~]# time for i in `seq 2000`; do ip netns exec gmk ip link show; done > /dev/null real 0m40.129s user 0m1.272s sys 0m3.898s Then I boot the kernel with maxcpus=1. Surprise! Surprise! It works fast. [ ~]# ip netns add gmk [ ~]# time for i in `seq 2000`; do ip netns exec gmk ip link show; done > /dev/null real 0m2.445s user 0m0.604s sys 0m1.778s > > Eric > _______________________________________________ > Containers mailing list > Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx > https://lists.linuxfoundation.org/mailman/listinfo/containers _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
