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Date: Mon, 30 Jan 2012 09:04:32 +0100 From: Eric Dumazet <eric.dumazet@...il.com> To: Or Gerlitz <ogerlitz@...lanox.com> Cc: Roland Dreier <roland@...nel.org>, Herbert Xu <herbert@...dor.apana.org.au>, davem@...emloft.net, linux-rdma <linux-rdma@...r.kernel.org>, Shlomo Pongratz <shlomop@...lanox.com>, netdev@...r.kernel.org Subject: Re: [PATCH 2/2] IB/ipoib: fix GRO merge failure for IPoIB originated TCP streams Le lundi 30 janvier 2012 à 09:44 +0200, Or Gerlitz a écrit : > On 1/30/2012 6:36 AM, Roland Dreier wrote: > > On Thu, Jan 26, 2012 at 6:43 AM, Or Gerlitz<ogerlitz@...lanox.com> wrote: > >> The GRO flow makes a check in every layer to ensure the packets > >> are actually merged only if they match at all layers. > >> > >> The first GRO check, at L2 always fails for IPoIB, since it assumes > >> that all packets have 14 bytes of Ethernet link layer header. Using the > >> IPoIB header will not help here either, since its only four bytes. To > >> overcome this, the skb mac header pointer is set to an area within the > >> packet IB GRH headroom, such that later, the L2 check done by GRO > >> succeeds and it can move to checks at the network and transport layers. > > > >> --- a/drivers/infiniband/ulp/ipoib/ipoib_ib.c > >> +++ b/drivers/infiniband/ulp/ipoib/ipoib_ib.c > >> @@ -286,10 +287,20 @@ static void ipoib_ib_handle_rx_wc(struct net_device *dev, struct ib_wc *wc) > >> else > >> skb->pkt_type = PACKET_MULTICAST; > >> > >> - skb_pull(skb, IB_GRH_BYTES); > >> + /* > >> + * GRO first does L2 compares (14 bytes). We must not let it start from > >> + * the IPoIB header as ten octets of the IP header, containing fields > >> + * which vary from packet to packet will cause non-merging of packets. > >> + * from the same TCP stream. > >> + */ > >> + psgid = skb_pull(skb, offsetof(struct ib_grh, sgid)); > >> + /* if there's no GRH, that area could contain random data */ > >> + if (!(wc->wc_flags& IB_WC_GRH)) > >> + memset(psgid, 0, 16); > >> + skb_reset_mac_header(skb); > >> + skb_pull(skb, IB_GRH_BYTES - offsetof(struct ib_grh, sgid)); > >> > >> skb->protocol = ((struct ipoib_header *) skb->data)->proto; > >> - skb_reset_mac_header(skb); > > > > This seems like a really weird place to fix this. Wouldn't it > > make more sense to fix the GRO check to handle non-ethernet L2 headers? > > Yes, we can do that as well. Herbert, Dave, would it be enough here, to > skip the Ethernet header and vlan comparison for skbs whose associated > netdevice type isn't ARPHRD_ETHER? e.g something along the lines of: > > > diff --git a/net/core/dev.c b/net/core/dev.c > > index 115dee1..c529f5a 100644 > > --- a/net/core/dev.c > > +++ b/net/core/dev.c > > @@ -3505,9 +3505,11 @@ __napi_gro_receive(struct napi_struct *napi, > > struct sk_buff *skb) > > unsigned long diffs; > > > > diffs = (unsigned long)p->dev ^ (unsigned long)skb->dev; > > - diffs |= p->vlan_tci ^ skb->vlan_tci; > > - diffs |= compare_ether_header(skb_mac_header(p), > > - skb_gro_mac_header(skb)); > > + if (!diffs && p->dev->type == ARPHRD_ETHER) { > > + diffs |= p->vlan_tci ^ skb->vlan_tci; > > + diffs |= compare_ether_header(skb_mac_header(p), > > + > > skb_gro_mac_header(skb)); > > + } > > NAPI_GRO_CB(p)->same_flow = !diffs; > > NAPI_GRO_CB(p)->flush = 0; Hmm, do we really need to compare ether header, thats the question. IMHO, GRO could avoid this check, as legal trafic could be never merged (eg multipath) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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