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Re: [PATCH net-next 2/2] firewire: net: set initial MTU = 1500 unconditionally, fix IPv6 on some CardBus cards

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On Sun, Oct 23, 2016 at 04:30:56PM +0200, Stefan Richter wrote:
> firewire-net, like the older eth1394 driver, reduced the initial MTU to
> less than 1500 octets if the local link layer controller's asynchronous
> packet reception limit was lower.
> 
> This is bogus, since this reception limit does not have anything to do
> with the transmission limit.  Neither did this reduction affect the TX
> path positively, nor could it prevent link fragmentation at the RX path.
> 
> Many FireWire CardBus cards have a max_rec of 9, causing an initial MTU
> of 1024 - 16 = 1008.  RFC 2734 and RFC 3146 allow a minimum max_rec = 8,
> which would result in an initial MTU of 512 - 16 = 496.  On such cards,
> IPv6 could only be employed if the MTU was manually increased to 1280 or
> more, i.e. IPv6 would not work without intervention from userland.
> 
> We now always initialize the MTU to 1500, which is the default according
> to RFC 2734 and RFC 3146.
> 
> On a VIA VT6316 based CardBus card which was affected by this, changing
> the MTU from 1008 to 1500 also increases TX bandwidth by 6 %.
> RX remains unaffected.
> 
> CC: netdev@vger.kernel.org
> CC: linux1394-devel@lists.sourceforge.net
> CC: Jarod Wilson <jarod@redhat.com>
> Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
> ---
>  drivers/firewire/net.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/drivers/firewire/net.c b/drivers/firewire/net.c
> index 99379542b263..03715e7d9d92 100644
> --- a/drivers/firewire/net.c
> +++ b/drivers/firewire/net.c
> @@ -1463,13 +1463,7 @@ static int fwnet_probe(struct fw_unit *unit,
>  		goto out;
>  	dev->local_fifo = dev->handler.offset;
>  
> -	/*
> -	 * Use the RFC 2734 default 1500 octets or the maximum payload
> -	 * as initial MTU
> -	 */
> -	net->mtu = min(1500U,
> -		       (1U << (card->max_receive + 1))
> -		       - RFC2374_FRAG_HDR_SIZE - IEEE1394_GASP_HDR_SIZE);
> +	net->mtu = 1500U;

Should be able to do just net->mtu = ETH_DATA_LEN;

-- 
Jarod Wilson
jarod@redhat.com

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[PATCH net-next 0/6] net: use core MTU range checking everywhere Jarod Wilson <jarod@redhat.com> - 2016-10-19 04:40 +0200
  [PATCH net-next 6/6] net: use core MTU range checking in misc drivers Jarod Wilson <jarod@redhat.com> - 2016-10-19 04:40 +0200
    Re: [PATCH net-next 6/6] net: use core MTU range checking in misc drivers Robin Holt <robinmholt@gmail.com> - 2016-10-19 16:40 +0200
    Re: [PATCH net-next 6/6] net: use core MTU range checking in misc  drivers Sabrina Dubroca <sd@queasysnail.net> - 2016-10-19 18:10 +0200
      Re: [PATCH net-next 6/6] net: use core MTU range checking in misc  drivers Stefan Richter <stefanr@s5r6.in-berlin.de> - 2016-10-20 00:50 +0200
        Re: [PATCH net-next 6/6] net: use core MTU range checking in misc  drivers Jarod Wilson <jarod@redhat.com> - 2016-10-20 05:20 +0200
          Re: [PATCH net-next 6/6] net: use core MTU range checking in misc  drivers Stefan Richter <stefanr@s5r6.in-berlin.de> - 2016-10-22 11:40 +0200
            Re: [PATCH net-next 6/6] net: use core MTU range checking in misc  drivers Stefan Richter <stefanr@s5r6.in-berlin.de> - 2016-10-22 21:00 +0200
  Re: [PATCH net-next 0/6] net: use core MTU range checking  everywhere David Miller <davem@davemloft.net> - 2016-10-19 21:20 +0200
    Re: [PATCH net-next 0/6] net: use core MTU range checking everywhere Jarod Wilson <jarod@redhat.com> - 2016-10-19 21:30 +0200
  [PATCH net-next v2 9/9] ipv4/6: use core net MTU range checking Jarod Wilson <jarod@redhat.com> - 2016-10-20 20:00 +0200
  [PATCH net-next v2 3/9] net: use core MTU range checking in wireless drivers Jarod Wilson <jarod@redhat.com> - 2016-10-20 20:00 +0200
    Re: [PATCH net-next v2 3/9] net: use core MTU range checking in  wireless drivers Johannes Berg <johannes@sipsolutions.net> - 2016-10-20 20:30 +0200
      Re: [PATCH net-next v2 3/9] net: use core MTU range checking in  wireless drivers David Miller <davem@davemloft.net> - 2016-10-20 20:50 +0200
  [PATCH net-next v2 1/9] ethernet: use net core MTU range checking in more drivers Jarod Wilson <jarod@redhat.com> - 2016-10-20 20:00 +0200
  [PATCH net-next v2 4/9] net: use core MTU range checking in WAN drivers Jarod Wilson <jarod@redhat.com> - 2016-10-20 20:00 +0200
  [PATCH net-next v2 2/9] net: use core MTU range checking in USB NIC drivers Jarod Wilson <jarod@redhat.com> - 2016-10-20 20:00 +0200
  [PATCH net-next v2 0/9] net: use core MTU range checking everywhere Jarod Wilson <jarod@redhat.com> - 2016-10-20 20:00 +0200
    [PATCH net-next v2 5/9] net: use core MTU range checking in core net infra Jarod Wilson <jarod@redhat.com> - 2016-10-20 20:00 +0200
    [PATCH net-next v2 6/9] net: use core MTU range checking in virt drivers Jarod Wilson <jarod@redhat.com> - 2016-10-20 20:00 +0200
      RE: [PATCH net-next v2 6/9] net: use core MTU range checking in virt  drivers Haiyang Zhang <haiyangz@microsoft.com> - 2016-10-20 20:10 +0200
        RE: [PATCH net-next v2 6/9] net: use core MTU range checking in virt  drivers "Kershner, David A" <David.Kershner@unisys.com> - 2016-10-20 22:50 +0200
      Re: [PATCH net-next v2 6/9] net: use core MTU range checking in virt  drivers "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-20 22:30 +0200
        Re: [PATCH net-next v2 6/9] net: use core MTU range checking in virt  drivers Jarod Wilson <jarod@redhat.com> - 2016-10-21 04:40 +0200
          Re: [PATCH net-next v2 6/9] net: use core MTU range checking in virt  drivers "Michael S. Tsirkin" <mst@redhat.com> - 2016-10-21 05:40 +0200
            Re: [PATCH net-next v2 6/9] net: use core MTU range checking in virt drivers Aaron Conole <aconole@bytheb.org> - 2016-10-21 15:30 +0200
      Re: [PATCH net-next v2 6/9] net: use core MTU range checking in virt  drivers Wei Liu <wei.liu2@citrix.com> - 2016-10-21 12:10 +0200
    [PATCH net-next v2 8/9] s390/net: use net core MTU range checking Jarod Wilson <jarod@redhat.com> - 2016-10-20 20:00 +0200
    [PATCH net-next v2 7/9] net: use core MTU range checking in misc drivers Jarod Wilson <jarod@redhat.com> - 2016-10-20 20:00 +0200
      Re: [PATCH net-next v2 7/9] net: use core MTU range checking in misc drivers Rémi Denis-Courmont <remi@remlab.net> - 2016-10-21 09:00 +0200
      Re: [PATCH net-next v2 7/9] net: use core MTU range checking in misc  drivers Sebastian Reichel <sre@kernel.org> - 2016-10-21 18:30 +0200
      Re: [net-next,v2,7/9] net: use core MTU range checking in misc drivers Sven Eckelmann <sven@narfation.org> - 2016-10-22 09:30 +0200
      Re: [PATCH net-next v2 7/9] net: use core MTU range checking in  misc drivers Stefan Richter <stefanr@s5r6.in-berlin.de> - 2016-10-22 21:20 +0200
        Re: [PATCH net-next v2 7/9] net: use core MTU range checking in  misc drivers Stefan Richter <stefanr@s5r6.in-berlin.de> - 2016-10-22 21:30 +0200
          Re: [PATCH net-next v2 7/9] net: use core MTU range checking in misc  drivers Jarod Wilson <jarod@redhat.com> - 2016-10-23 03:20 +0200
            [PATCH net-next 1/2] firewire: net: fix maximum possible MTU Stefan Richter <stefanr@s5r6.in-berlin.de> - 2016-10-23 16:30 +0200
              [PATCH net-next 2/2] firewire: net: set initial MTU = 1500  unconditionally, fix IPv6 on some CardBus cards Stefan Richter <stefanr@s5r6.in-berlin.de> - 2016-10-23 16:40 +0200
                Re: [PATCH net-next 2/2] firewire: net: set initial MTU = 1500  unconditionally, fix IPv6 on some CardBus cards Jarod Wilson <jarod@redhat.com> - 2016-10-24 04:00 +0200
                [PATCH net-next 2/2 v2] firewire: net: set initial MTU = 1500  unconditionally, fix IPv6 on some CardBus cards Stefan Richter <stefanr@s5r6.in-berlin.de> - 2016-10-24 14:30 +0200
                Re: [PATCH net-next 2/2 v2] firewire: net: set initial MTU = 1500  unconditionally, fix IPv6 on some CardBus cards Jarod Wilson <jarod@redhat.com> - 2016-10-25 05:10 +0200
                Re: [PATCH net-next 2/2] firewire: net: set initial MTU = 1500  unconditionally, fix IPv6 on some CardBus cards David Miller <davem@davemloft.net> - 2016-10-26 23:40 +0200
              Re: [PATCH net-next 1/2] firewire: net: fix maximum possible MTU Jarod Wilson <jarod@redhat.com> - 2016-10-24 04:00 +0200
              Re: [PATCH net-next 1/2] firewire: net: fix maximum possible MTU David Miller <davem@davemloft.net> - 2016-10-26 23:40 +0200
    Re: [PATCH net-next v2 0/9] net: use core MTU range checking  everywhere David Miller <davem@davemloft.net> - 2016-10-20 21:00 +0200

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