netdev.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Hangbin Liu <liuhangbin@gmail.com>
To: David Miller <davem@davemloft.net>
Cc: netdev@vger.kernel.org, ja@ssi.bg, marcelo.leitner@gmail.com,
	dsahern@gmail.com, edumazet@google.com,
	Guillaume Nault <gnault@redhat.com>
Subject: Re: [PATCHv2 net] ipv6/route: should not update neigh confirm time during PMTU update
Date: Tue, 10 Dec 2019 11:36:56 +0800	[thread overview]
Message-ID: <20191210033656.GM18865@dhcp-12-139.nay.redhat.com> (raw)
In-Reply-To: <20191203.115818.1902434596879929857.davem@davemloft.net>

Hi David,

Sorry for the late reply. Hope you still have impression for this discussion.
I discussed this issue with my colleagues offline and I still have some questions.
Please see comments below.

On Tue, Dec 03, 2019 at 11:58:18AM -0800, David Miller wrote:
> >> > That's not what I said.
> >> > 
> >> > I said that this interface is designed for situations where the neigh
> >> > update is appropriate, and that's what happens for most callers _except_
> >> > these tunnel cases.
> >> > 
> >> > The tunnel use is the exception and invoking the interface
> >> > inappropriately.
> >> > 
> >> > It is important to keep the neigh reachability fresh for TCP flows so
> >> > you cannot remove this dst_confirm_neigh() call.

The first is why IPv4 don't need this neigh update. I didn't
find dst_confirm_neigh() or ipv4_confirm_neigh() in ip_rt_update_pmtu()

> > 
> > I have one question here. Since we have the .confirm_neigh fuction in
> > struct dst_ops. How about do a dst->ops->confirm_neigh() separately after
> > dst->ops->update_pmtu()? Why should we mix the confirm_neigh() in
> > update_pmtu(), like ip6_rt_update_pmtu()?
> 
> Two indirect calls which have high cost due to spectre mitigation?

Guillaume pointed me that dst_confirm_neigh() is also a indriect call.
So it should take same cost to call dst_confirm_neigh() in or before
__ip6_rt_update_pmtu(). If they are the same cose, I think there would
have two fixes.

1. Add a new parameter 'bool confirm_neigh' to __ip6_rt_update_pmtu(),
update struct dst_ops.update_mtu and all functions who called it.

2. Move dst_confirm_neigh() out of __ip6_rt_update_pmtu() and only call it
   in fuctions who need it, like inet6_csk_update_pmtu().

What do you think? Please tell me if I missed something.

Regards
Hangbin

  reply	other threads:[~2019-12-10  3:37 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-22  6:19 [PATCH net] ipv6/route: only update neigh confirm time if pmtu changed Hangbin Liu
2019-11-22 18:04 ` David Miller
2019-11-26  9:17   ` Hangbin Liu
2019-12-03  2:11 ` [PATCHv2 net] ipv6/route: should not update neigh confirm time during PMTU update Hangbin Liu
2019-12-03  2:47   ` David Miller
2019-12-03 10:15     ` Hangbin Liu
2019-12-03 10:25       ` Hangbin Liu
2019-12-03 19:58         ` David Miller
2019-12-10  3:36           ` Hangbin Liu [this message]
2019-12-10 17:00             ` Guillaume Nault
2019-12-18 11:53   ` [PATCH net-next 0/8] disable neigh update for tunnels during pmtu update Hangbin Liu
2019-12-18 11:53     ` [PATCH net-next 1/8] net: add bool confirm_neigh parameter for dst_ops.update_pmtu Hangbin Liu
2019-12-18 11:53     ` [PATCH net-next 2/8] ip6_gre: do not confirm neighbor when do pmtu update Hangbin Liu
2019-12-18 11:53     ` [PATCH net-next 3/8] gtp: " Hangbin Liu
2019-12-18 11:53     ` [PATCH net-next 4/8] net/dst: add new function skb_dst_update_pmtu_no_confirm Hangbin Liu
2019-12-18 11:53     ` [PATCH net-next 5/8] tunnel: do not confirm neighbor when do pmtu update Hangbin Liu
2019-12-19 17:47       ` Guillaume Nault
2019-12-20  2:36         ` Hangbin Liu
2019-12-18 11:53     ` [PATCH net-next 6/8] vti: " Hangbin Liu
2019-12-18 11:53     ` [PATCH net-next 7/8] sit: " Hangbin Liu
2019-12-18 11:53     ` [PATCH net-next 8/8] net/dst: do not confirm neighbor for vxlan and geneve " Hangbin Liu
2019-12-19 17:49       ` Guillaume Nault
2019-12-18 12:01     ` [PATCH net-next 0/8] disable neigh update for tunnels during " Hangbin Liu
2019-12-19 17:57       ` Guillaume Nault
2019-12-20  2:48         ` Hangbin Liu
2019-12-19 17:53     ` Guillaume Nault
2019-12-20  3:25     ` [PATCHv4 net " Hangbin Liu
2019-12-20  3:25       ` [PATCHv4 net 1/8] net: add bool confirm_neigh parameter for dst_ops.update_pmtu Hangbin Liu
2019-12-20  3:25       ` [PATCHv4 net 2/8] ip6_gre: do not confirm neighbor when do pmtu update Hangbin Liu
2019-12-20  3:25       ` [PATCHv4 net 3/8] gtp: " Hangbin Liu
2019-12-21 18:35         ` Guillaume Nault
2019-12-20  3:25       ` [PATCHv4 net 4/8] net/dst: add new function skb_dst_update_pmtu_no_confirm Hangbin Liu
2019-12-20  3:25       ` [PATCHv4 net 5/8] tunnel: do not confirm neighbor when do pmtu update Hangbin Liu
2019-12-21 18:43         ` Guillaume Nault
2019-12-20  3:25       ` [PATCHv4 net 6/8] vti: " Hangbin Liu
2019-12-21 18:30         ` Guillaume Nault
2019-12-20  3:25       ` [PATCHv4 net 7/8] sit: " Hangbin Liu
2019-12-20  3:25       ` [PATCHv4 net 8/8] net/dst: do not confirm neighbor for vxlan and geneve " Hangbin Liu
2019-12-21 18:38         ` Guillaume Nault
2019-12-20 16:14       ` [PATCHv4 net 0/8] disable neigh update for tunnels during " David Ahern
2019-12-22  2:51       ` [PATCHv5 " Hangbin Liu
2019-12-22  2:51         ` [PATCHv5 net 1/8] net: add bool confirm_neigh parameter for dst_ops.update_pmtu Hangbin Liu
2019-12-22  2:51         ` [PATCHv5 net 2/8] ip6_gre: do not confirm neighbor when do pmtu update Hangbin Liu
2019-12-22  2:51         ` [PATCHv5 net 3/8] gtp: " Hangbin Liu
2019-12-22  2:51         ` [PATCHv5 net 4/8] net/dst: add new function skb_dst_update_pmtu_no_confirm Hangbin Liu
2019-12-22  2:51         ` [PATCHv5 net 5/8] tunnel: do not confirm neighbor when do pmtu update Hangbin Liu
2019-12-22  2:51         ` [PATCHv5 net 6/8] vti: " Hangbin Liu
2019-12-22  2:51         ` [PATCHv5 net 7/8] sit: " Hangbin Liu
2019-12-22  2:51         ` [PATCHv5 net 8/8] net/dst: do not confirm neighbor for vxlan and geneve " Hangbin Liu
2019-12-22 22:10         ` [PATCHv5 net 0/8] disable neigh update for tunnels during " Guillaume Nault
2019-12-25  6:30         ` David Miller

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20191210033656.GM18865@dhcp-12-139.nay.redhat.com \
    --to=liuhangbin@gmail.com \
    --cc=davem@davemloft.net \
    --cc=dsahern@gmail.com \
    --cc=edumazet@google.com \
    --cc=gnault@redhat.com \
    --cc=ja@ssi.bg \
    --cc=marcelo.leitner@gmail.com \
    --cc=netdev@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).