netdev - Re: igmp: Staggered igmp report intervals for unsolicited igmp reports

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Message-ID: <20100922215052.GK11157@obsidianresearch.com>
Date:	Wed, 22 Sep 2010 15:50:52 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	David Stevens <dlstevens@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
	Bob Arendt <rda@...con.com>
Subject: Re: igmp: Staggered igmp report intervals for unsolicited igmp
	reports

On Wed, Sep 22, 2010 at 02:58:15PM -0500, Christoph Lameter wrote:
> > packets if it isn't ready quickly? A querier is what makes these
> > reliable, but for the start-up in particular, I think it'd be better
> > to not initiate the send on devices that have this problem until the
> > device is actually ready to send-- why not put the delay in the device
> > driver on initialization?
> 
> The device is ready. Its just the multicast group that has not been
> established yet.

In IB when the SA replies to a group join the group should be ready,
prior to that the device can't send into the group because it has no
MLID for the group.. If you have a MLID then the group is working.

Is the issue you are dropping IGMP packets because the 224.0.0.2 join
hasn't finished? Ideally you'd wait for the SA to reply before sending
a IGMP, but a simpler solution might just be to use the broadcast MLID
for packets addressed to a MGID that has not yet got a MLID. This
would bebe similar to the ethernet behaviour of flooding.

Jason
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