From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752509AbaH1UrF (ORCPT ); Thu, 28 Aug 2014 16:47:05 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:53895 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751633AbaH1UrD (ORCPT ); Thu, 28 Aug 2014 16:47:03 -0400 Date: Thu, 28 Aug 2014 13:46:58 -0700 From: "Paul E. McKenney" To: "Eric W. Biederman" Cc: Simon Kirby , linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: net_ns cleanup / RCU overhead Message-ID: <20140828204658.GL5001@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20140820055855.GB5579@hostway.ca> <20140828192431.GF5001@linux.vnet.ibm.com> <20140828194422.GB8867@hostway.ca> <87oav4l5g9.fsf@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87oav4l5g9.fsf@x220.int.ebiederm.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14082820-1542-0000-0000-00000460818B Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 28, 2014 at 03:33:42PM -0500, Eric W. Biederman wrote: > Simon Kirby writes: > > > On Thu, Aug 28, 2014 at 12:24:31PM -0700, Paul E. McKenney wrote: > > > >> On Tue, Aug 19, 2014 at 10:58:55PM -0700, Simon Kirby wrote: > >> > Hello! > >> > > >> > In trying to figure out what happened to a box running lots of vsftpd > >> > since we deployed a CONFIG_NET_NS=y kernel to it, we found that the > >> > (wall) time needed for cleanup_net() to complete, even on an idle box, > >> > can be quite long: > >> > > >> > #!/bin/bash > >> > > >> > ip netns delete test >&/dev/null > >> > while ip netns add test; do > >> > echo hi > >> > ip netns delete test > >> > done > >> > > >> > On my desktop and typical hosts, this prints at only around 4 or 6 per > >> > second. While this is happening, "vmstat 1" reports 100% idle, and there > >> > there are D-state processes with stacks similar to: > >> > > >> > 30566 [kworker/u16:1] D wait_rcu_gp+0x48, synchronize_sched+0x2f, cleanup_net+0xdb, process_one_work+0x175, worker_thread+0x119, kthread+0xbb, ret_from_fork+0x7c, 0xffffffffffffffff > >> > > >> > 32220 ip D copy_net_ns+0x68, create_new_namespaces+0xfc, unshare_nsproxy_namespaces+0x66, SyS_unshare+0x159, system_call_fastpath+0x16, 0xffffffffffffffff > >> > > >> > copy_net_ns() is waiting on net_mutex which is held by cleanup_net(). > >> > > >> > vsftpd uses CLONE_NEWNET to set up privsep processes. There is a comment > >> > about it being really slow before 2.6.35 (it avoids CLONE_NEWNET in that > >> > case). I didn't find anything that makes 2.6.35 any faster, but on Debian > >> > 2.6.36-5-amd64, I notice it does seem to be a bit faster than 3.2, 3.10, > >> > 3.16, though still not anything I'd ever want to rely on per connection. > >> > > >> > C implementation of the above: http://0x.ca/sim/ref/tools/netnsloop.c > >> > > >> > Kernel stack "top": http://0x.ca/sim/ref/tools/pstack > >> > > >> > What's going on here? > >> > >> That is a bit slow for many configurations, but there are some exceptions. > >> > >> So, what is your kernel's .config? > > > > I was unable to find a config (or stock kernel) that was any different, > > but here's the one we're using: http://0x.ca/sim/ref/3.10/config-3.10.53 > > > > How fast does the above test run for you? > > > > We've been running with the attached, which has helped a little, but it's > > still quite slow in our particular use case (vsftpd), and with the above > n> test. Should I enable RCU_TRACE or STALL_INFO with a low timeout or > > something? > > I just want to add a little bit more analysis to this. > > What we desire to be fast is the copy_net_ns, cleanup_net is batched and > asynchronous which nothing really cares how long it takes except that > cleanup_net holds the net_mutex and thus blocks copy_net_ns. > > The puzzle is why and which rcu delays Simon is seeing in the network > namespace cleanup path, as it seems like the synchronize_rcu is not > the only one, and in the case of vsftp with trivail network namespaces > where nothing has been done we should not need to delay. Indeed, given the version and .config, I can't see why any individual RCU grace-period operation would be particularly slow. I suggest using ftrace on synchronize_rcu() and friends. Thanx, Paul > Eric > > > > Simon- > > > > -- >8 -- > > Subject: [PATCH] netns: use synchronize_rcu_expedited instead of > > synchronize_rcu > > > > Similar to ef323088, with synchronize_rcu(), we are only able to create > > and destroy about 4 or 7 net namespaces per second, which really puts a > > dent in the performance of programs attempting to use CLONE_NEWNET for > > privilege separation (vsftpd, chromium). > > --- > > net/core/net_namespace.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c > > index 85b6269..6dcb4b3 100644 > > --- a/net/core/net_namespace.c > > +++ b/net/core/net_namespace.c > > @@ -296,7 +296,7 @@ static void cleanup_net(struct work_struct *work) > > * This needs to be before calling the exit() notifiers, so > > * the rcu_barrier() below isn't sufficient alone. > > */ > > - synchronize_rcu(); > > + synchronize_rcu_expedited(); > > > > /* Run all of the network namespace exit methods */ > > list_for_each_entry_reverse(ops, &pernet_list, list) >