netdev - Re: [IPoIB] Identify multicast packets and fix IGMP breakage V3

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Date:	Fri, 27 Aug 2010 08:29:38 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
cc:	Roland Dreier <rdreier@...co.com>, linux-rdma@...r.kernel.org,
	ogerlitz@...taire.com, yosefe@...taire.com, netdev@...r.kernel.org,
	David Miller <davem@...emloft.net>
Subject: Re: [IPoIB] Identify multicast packets and fix IGMP breakage V3

On Thu, 26 Aug 2010, Jason Gunthorpe wrote:

> I think doing the memcmp only in the multicast path should be
> reasonable overhead wise.

Ok the dgid is only 8 bytes not the whole 40 bytes.... Here is the patch
somewhat cleaned up with PACKET_BROADCAST.


Subject: [IPoIB] Identify multicast packets and fix IGMP breakage V3

IGMP processing is broken because the IPOIB does not set the
skb->pkt_type the right way for Multicast traffic. All incoming
packets are set to PACKET_HOST which means that the igmp_recv()
function will ignore the IGMP broadcasts/multicasts.

This in turn means that the IGMP timers are firing and are sending
information about multicast subscriptions unnecessarily. In a large
private network this can cause traffic spikes.

Signed-off-by: Christoph Lameter <cl@...ux.com>

---

Index: linux-2.6/drivers/infiniband/ulp/ipoib/ipoib_ib.c
===================================================================
--- linux-2.6.orig/drivers/infiniband/ulp/ipoib/ipoib_ib.c	2010-08-26 18:24:07.842079559 -0500
+++ linux-2.6/drivers/infiniband/ulp/ipoib/ipoib_ib.c	2010-08-27 08:26:37.929641162 -0500
@@ -223,6 +223,7 @@
 	unsigned int wr_id = wc->wr_id & ~IPOIB_OP_RECV;
 	struct sk_buff *skb;
 	u64 mapping[IPOIB_UD_RX_SG];
+	union ib_gid *dgid;

 	ipoib_dbg_data(priv, "recv completion: id %d, status: %d\n",
 		       wr_id, wc->status);
@@ -271,6 +272,21 @@
 	ipoib_ud_dma_unmap_rx(priv, mapping);
 	ipoib_ud_skb_put_frags(priv, skb, wc->byte_len);

+	/* First byte of dgid signals multicast when 0xff */
+	dgid = &((struct ib_grh *)skb->data)->dgid;
+
+	if (!(wc->wc_flags & IB_WC_GRH) || dgid->raw[0] != 0xff)
+
+		skb->pkt_type = PACKET_HOST;
+
+	else if (memcmp(dgid, dev->broadcast + 4, sizeof(union ib_gid)) == 0)
+
+		skb->pkt_type = PACKET_BROADCAST;
+
+	else
+
+		skb->pkt_type = PACKET_MULTICAST;
+
 	skb_pull(skb, IB_GRH_BYTES);

 	skb->protocol = ((struct ipoib_header *) skb->data)->proto;
@@ -281,9 +297,6 @@
 	dev->stats.rx_bytes += skb->len;

 	skb->dev = dev;
-	/* XXX get correct PACKET_ type here */
-	skb->pkt_type = PACKET_HOST;
-
 	if (test_bit(IPOIB_FLAG_CSUM, &priv->flags) && likely(wc->csum_ok))
 		skb->ip_summed = CHECKSUM_UNNECESSARY;

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