Rafael David Tinoco <rafael.tin...@canonical.com> writes: > Hello Eric, > > Coming back to this... > > On Jun 16, 2014, at 12:01 PM, Rafael Tinoco <rafael.tin...@canonical.com> > wrote: > >> ... >> >> On Fri, Jun 13, 2014 at 9:02 PM, Eric W. Biederman >> <ebied...@xmission.com> wrote: >>> Rafael Tinoco <rafael.tin...@canonical.com> writes: >>> >>>> Okay, >>>> >>>> Tests with the same script were done. >>>> I'm comparing : master + patch vs 3.15.0-rc5 (last sync'ed rcu commit) >>>> and 3.9 last bisect good. >>>> >>>> Same tests were made. I'm comparing the following versions: >>>> >>>> 1) master + suggested patch >>>> 2) 3.15.0-rc5 (last rcu commit in my clone) >>>> 3) 3.9-rc2 (last bisect good) >>> >>> I am having a hard time making sense of your numbers. >>> >>> If I have read your email correctly my suggested patch caused: >>> "ip netns add" numbers to improve >>> 1x "ip netns exec" to improve some >>> 2x "ip netns exec" to show no improvement >>> "ip link add" to show no effect (after the 2x ip netns exec) >> >> - "netns add" are as good as they were before this regression. >> - "netns exec" are improved but still 50% of the last good bisect commit. >> - "link add" didn't show difference. >> >>> This is interesting in a lot of ways. >>> - This seems to confirm that the only rcu usage in ip netns add >>> was switch_task_namespaces. Which is convinient as that rules >>> out most of the network stack when looking for performance oddities. >>> >>> - "ip netns exec" had an expected performance improvement >>> - "ip netns exec" is still slow (so something odd is still going on) >>> - "ip link add" appears immaterial to the performance problem. >>> >>> It would be interesting to switch the "ip link add" and "ip netns exec" >>> in your test case to confirm that there is nothing interesting/slow >>> going on in "ip link add" >> >> - will do that. > > IP link add seems ok. > >> >>> >>> Which leaves me with the question what ip "ip netns exec" remains >>> that is using rcu and is slowing all of this down. >> >> - will check this also. > > Based on my tests (and some other users that deployed this patch on a server > farm) > it looks like changing rcu_read_lock() to task_lock() did the trick. We are > getting > same (sometimes much better) results - comparing bisect good - for a big > amount > of netns being created simultaneously. > > Is it possible to make this change permanent in kernel tree ?
Definitely. I just need to finish getting my act together. It sounded like you had seen other performance problems and I was waiting on your futher testing so we could narrow down. If you can't see other problems then I am happy to move forward with this. Thank you for testing and reporting this, Eric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
