netdev - Re: IPoIB: Fix multicast packet drops before join is complete

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Date:	Fri, 12 Jun 2009 10:17:27 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>
cc:	rdreier@...co.com, netdev@...r.kernel.org, yosefe@...taire.COM
Subject: Re: IPoIB: Fix multicast packet drops before join is complete

On Thu, 11 Jun 2009, David Miller wrote:

> > Umm?? My patch does that....
>
> No it does not.  It eliminates a limit on the generic intermediate
> queue.  It did no blocking, no sleeping, or the process when it
> joined the group.

What intermediate queue? The check in the IPoIB layuer was simply for
packets queued on a socket. Are you talking about the TX ring?

> I was suggesting to block the process, at socket context time, when it
> joins a multicast group.  That way it wouldn't be able to do any sends
> until IPoIB could resolve the multicast join.

My patch blocks the process when the queue has filled up. It blocks when
the queue has reached sk_sndbuf

The join occurs and then the app continues sending packets that are
queued until the queue limits have been reached. Then the process blocks.

It would be better to block earlier but this also does the trick.
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