Hi Eric/Andrew, Thanks for your response. I have commented out the synchronize_rcu() in namespace_unlock() which is located in /fs/namespace.c namespace_unlock() now am able to see the result in fraction of seconds. Regards Madhu On Thu, Aug 4, 2016 at 11:51 AM, Andrew Vagin <avagin@xxxxxxxxx> wrote: > On Wed, Aug 03, 2016 at 06:14:02PM -0700, Andrew Vagin wrote: > > 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. > > > > [snip] > > > [ ~]# 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 > > This degradations is due to synchronize_rcu() in namespace_unlock(), > which was added in 48a066e72d9 ("RCU'd vfsmounts"). > > Here is timings for all calls during sys_unshare(): > https://gist.github.com/avagin/3811fbbb553795a78fc6ae602f86866a > > > > > > > > > > > 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