From: Florian Fainelli <f.fainelli@gmail.com>
To: Vladimir Oltean <olteanv@gmail.com>,
andrew@lunn.ch, vivien.didelot@gmail.com, davem@davemloft.net,
jakub.kicinski@netronome.com
Cc: murali.policharla@broadcom.com, stephen@networkplumber.org,
jiri@resnulli.us, idosch@idosch.org, kuba@kernel.org,
nikolay@cumulusnetworks.com, netdev@vger.kernel.org
Subject: Re: [PATCH v2 net-next 10/10] net: bridge: implement auto-normalization of MTU for hardware datapath
Date: Wed, 25 Mar 2020 16:17:54 -0700 [thread overview]
Message-ID: <8d2d819c-328c-9b2a-d25b-dccc85b93735@gmail.com> (raw)
In-Reply-To: <20200325152209.3428-11-olteanv@gmail.com>
On 3/25/2020 8:22 AM, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
>
> In the initial attempt to add MTU configuration for DSA:
>
> https://patchwork.ozlabs.org/cover/1199868/
>
> Florian raised a concern about the bridge MTU normalization logic (when
> you bridge an interface with MTU 9000 and one with MTU 1500). His
> expectation was that the bridge would automatically change the MTU of
> all its slave ports to the minimum MTU, if those slaves are part of the
> same hardware bridge. However, it doesn't do that, and for good reason,
> I think. What br_mtu_auto_adjust() does is it adjusts the MTU of the
> bridge net device itself, and not that of any slave port. If it were to
> modify the MTU of the slave ports, the effect would be that the user
> wouldn't be able to increase the MTU of any bridge slave port as long as
> it was part of the bridge, which would be a bit annoying to say the
> least.
>
> The idea behind this behavior is that normal termination from Linux over
> the L2 forwarding domain described by DSA should happen over the bridge
> net device, which _is_ properly limited by the minimum MTU. And
> termination over individual slave device is possible even if those are
> bridged. But that is not "forwarding", so there's no reason to do
> normalization there, since only a single interface sees that packet.
>
> The real problem is with the offloaded data path, where of course, the
> bridge net device MTU is ignored. So a packet received on an interface
> with MTU 9000 would still be forwarded to an interface with MTU 1500.
> And that is exactly what this patch is trying to prevent from happening.
>
> Florian's idea was that all hardware ports having the same
> netdev_port_same_parent_id should be adjusted to have the same MTU.
> The MTU that we attempt to configure the ports to is the most recently
> modified MTU. The attempt is to follow user intention as closely as
> possible and not be annoying at that.
>
> So there are 2 cases really:
>
> ip link set dev sw0p0 master br0
> ip link set dev sw0p1 mtu 1400
> ip link set dev sw0p1 master br0
>
> The above sequence will make sw0p0 inherit MTU 1400 as well.
>
> The second case:
>
> ip link set dev sw0p0 master br0
> ip link set dev sw0p1 master br0
> ip link set dev sw0p0 mtu 1400
>
> This sequence will make sw0p1 inherit MTU 1400 from sw0p0.
>
> Suggested-by: Florian Fainelli <f.fainelli@gmail.com>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
> ---
> net/bridge/br.c | 1 +
> net/bridge/br_if.c | 93 +++++++++++++++++++++++++++++++++++++++++
> net/bridge/br_private.h | 1 +
> 3 files changed, 95 insertions(+)
>
> diff --git a/net/bridge/br.c b/net/bridge/br.c
> index b6fe30e3768f..5f05380df1ee 100644
> --- a/net/bridge/br.c
> +++ b/net/bridge/br.c
> @@ -57,6 +57,7 @@ static int br_device_event(struct notifier_block *unused, unsigned long event, v
>
> switch (event) {
> case NETDEV_CHANGEMTU:
> + br_mtu_normalization(br, dev);
I do not remember if you are allowed to sleep in a netdevice notifier, I
believe not, so you may need to pass a gfp_t to br_mtu_normalization for
allocations to be GFP_ATOMIC when called from that context, and
GFP_KERNEL from br_add_if().
It would be nice if we could avoid doing these allocations when called
from the netdev notifier though, could we just keep the information
around since the br_hw_port follows the same lifetime as the
net_bridge_port structure. Other than that, this looks good to me, thanks!
--
Florian
next prev parent reply other threads:[~2020-03-25 23:18 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-25 15:21 [PATCH v2 net-next 00/10] Configure the MTU on DSA switches Vladimir Oltean
2020-03-25 15:22 ` [PATCH v2 net-next 01/10] net: dsa: configure the MTU for switch ports Vladimir Oltean
2020-03-25 15:22 ` [PATCH v2 net-next 02/10] net: phy: bcm7xx: Add jumbo frame configuration to PHY Vladimir Oltean
2020-03-25 15:44 ` Heiner Kallweit
2020-03-25 22:45 ` Vladimir Oltean
2020-03-25 23:02 ` Florian Fainelli
2020-03-25 23:21 ` Heiner Kallweit
2020-03-25 15:22 ` [PATCH v2 net-next 03/10] bgmac: Add support for Jumbo frames Vladimir Oltean
2020-03-25 15:22 ` [PATCH v2 net-next 04/10] bgmac: Add MTU configuration support to the driver Vladimir Oltean
2020-03-25 15:22 ` [PATCH v2 net-next 05/10] bgmac: Add DMA support to handle frames beyond 8192 bytes Vladimir Oltean
2020-03-25 23:07 ` Florian Fainelli
2020-03-25 15:22 ` [PATCH v2 net-next 06/10] net: dsa: b53: Add MTU configuration support Vladimir Oltean
2020-03-25 23:21 ` Florian Fainelli
2020-03-26 0:48 ` Vladimir Oltean
2020-03-25 15:22 ` [PATCH v2 net-next 07/10] net: dsa: sja1105: Implement the port MTU callbacks Vladimir Oltean
2020-03-25 23:08 ` Florian Fainelli
2020-03-25 15:22 ` [PATCH v2 net-next 08/10] net: dsa: vsc73xx: Make the MTU configurable Vladimir Oltean
2020-03-25 23:09 ` Florian Fainelli
2020-03-25 15:22 ` [PATCH v2 net-next 09/10] net: dsa: felix: support changing the MTU Vladimir Oltean
2020-03-25 23:10 ` Florian Fainelli
2020-03-25 15:22 ` [PATCH v2 net-next 10/10] net: bridge: implement auto-normalization of MTU for hardware datapath Vladimir Oltean
2020-03-25 23:17 ` Florian Fainelli [this message]
2020-03-26 0:30 ` Vladimir Oltean
2020-03-26 10:17 ` Ido Schimmel
2020-03-26 10:25 ` Vladimir Oltean
2020-03-26 11:35 ` Ido Schimmel
2020-03-26 11:44 ` Vladimir Oltean
2020-03-26 11:54 ` Ido Schimmel
2020-03-26 12:34 ` Vladimir Oltean
2020-03-26 12:59 ` Ido Schimmel
2020-03-26 12:06 ` Nikolay Aleksandrov
2020-03-26 12:18 ` Vladimir Oltean
2020-03-26 12:19 ` Nikolay Aleksandrov
2020-03-26 12:25 ` Vladimir Oltean
2020-03-26 12:38 ` Nikolay Aleksandrov
2020-03-26 18:49 ` Jakub Kicinski
2020-03-26 19:41 ` Nikolay Aleksandrov
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=8d2d819c-328c-9b2a-d25b-dccc85b93735@gmail.com \
--to=f.fainelli@gmail.com \
--cc=andrew@lunn.ch \
--cc=davem@davemloft.net \
--cc=idosch@idosch.org \
--cc=jakub.kicinski@netronome.com \
--cc=jiri@resnulli.us \
--cc=kuba@kernel.org \
--cc=murali.policharla@broadcom.com \
--cc=netdev@vger.kernel.org \
--cc=nikolay@cumulusnetworks.com \
--cc=olteanv@gmail.com \
--cc=stephen@networkplumber.org \
--cc=vivien.didelot@gmail.com \
/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).