This was talked about before (e.g. https://lkml.org/lkml/2014/6/11/42)
In 3.10, this 'script' takes ~1s to run, regardless of # CPU: ip netns add foo ip netns add bar for i in `seq 0 1000` do echo -e 'netns exec foo echo\nnetns exec bar echo' >> ipnetns.batch done time ip -b ipnetns.batch > /dev/null On 3.16... 4.12rc5, it gets very slow as you add CPU. 1cpu: 0m1.3 12cpu: 1m36 32cpu: 2m36 72cpu: 3m50 if you have a 2nd copy of it running (e.g .contention) it gets much much worse. this is in turn causing me an issue in OpenStack Neutron l3-agent, which creates/destroys/enters namespaces for DHCP, Router. I had a few shots in the dark of tuning e.g. rcu_nocbs= [tried 0, 1-31, etc]. The commit that was talked about as fixing, 728dba3a39c66b3d8ac889ddbe38b5b1c264aec3, doesn't seem to have helped me. I have tried this on Centos7 and Ubuntu 16.10+ kernel configs. Some work was done characterising this linked https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1328088 Does anyone have a suggestion?
