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 ? Much appreciate your attention Eric Regards Rafael Tinoco > >> Eric > > Tks > > Rafael -- 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/
