netdev - Re: [PATCH 1/2] net: igmp: Reduce Unsolicited report interval to 1s when using IGMPv3

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Message-ID: <20130726163913.GG3890@order.stressinduktion.org>
Date:	Fri, 26 Jul 2013 18:39:13 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	William Manley <william.manley@...view.com>,
	netdev@...r.kernel.org, bcrl@...ck.org, luky-37@...mail.com,
	sergei.shtylyov@...entembedded.com, bhutchings@...arflare.com,
	davem@...emloft.net
Subject: Re: [PATCH 1/2] net: igmp: Reduce Unsolicited report interval to 1s when using IGMPv3

On Fri, Jul 26, 2013 at 06:32:39PM +0200, Hannes Frederic Sowa wrote:
> On Thu, Jul 25, 2013 at 01:14:04PM +0100, William Manley wrote:
> > If an IGMP join packet is lost you will not receive data sent to the
> > multicast group so if no data arrives from that multicast group in a
> > period of time after the IGMP join a second IGMP join will be sent.  The
> > delay between joins is the "IGMP Unsolicited Report Interval".
> > 
> > Previously this value was hard coded to be chosen randomly between 0-10s.
> > This can be too long for some use-cases, such as IPTV as it can cause
> > channel change to be slow in the presence of packet loss.
> > 
> > The value 10s has come from IGMPv2 RFC2236, which was reduced to 1s in
> > IGMPv3 RFC3376.  This patch makes the kernel use the 1s value from the
> > later RFC if we are operating in IGMPv3 mode.  IGMPv2 behaviour is
> > unaffected.
> > 
> > Tested with Wireshark and a simple program to join a (non-existent)
> > multicast group.  The distribution of timings for the second join differ
> > based upon setting /proc/sys/net/ipv4/conf/eth0/force_igmp_version.
> >
> > [...]
> >
>
> [...]
> 
> Otherwise I am fine with it.

Also, could you have a look at IPv6, too? We currently use a hardcoded
IGMP6_UNSOLICITED_IVAL = 10*HZ there.

Thanks,

  Hannes

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