netdev - Re: ICMP packets - ll_temac with Microblaze

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Date:	Wed, 21 Dec 2011 16:44:45 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	monstr@...str.eu
Cc:	David Miller <davem@...emloft.net>,
	John Williams <john.williams@...alogix.com>,
	netdev@...r.kernel.org
Subject: Re: ICMP packets - ll_temac with Microblaze

Le mercredi 21 décembre 2011 à 16:30 +0100, Eric Dumazet a écrit :
> Le mercredi 21 décembre 2011 à 15:24 +0100, Michal Simek a écrit :
> > Eric Dumazet wrote:
> > > Le mercredi 21 décembre 2011 à 14:28 +0100, Michal Simek a écrit :
> > > 
> > >> ok. Can you provide me any background why size should be setup by
> > >> size = SKB_WITH_OVERHEAD(ksize(data));
> > >> and not to use size which is passed to kmalloc in __alloc_skb.
> > > 
> > > Its all about memory accounting (based on skb->truesize)
> > > 
> > > Prior to the patch, we could fool memory accounting because skbs claimed
> > > to use less memory than what they really used.
> > > 
> > > And crash machines eventually.
> > > 
> > > Now memory accouting is fixed, we probably need to change some points in
> > > the kernel, where we previously accepted a small skb, but not a very
> > > large one.
> > > 
> > > Since "ping" probably uses SOCK_RAW sockets, I'll try this one :
> > > 
> > > (We dont care of _this_ skb truesize, only on the count of previously
> > > queued packets)
> > > 
> > > 
> > > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> > > index 0da505c..a809a48 100644
> > > --- a/net/packet/af_packet.c
> > > +++ b/net/packet/af_packet.c
> > > @@ -1631,8 +1631,7 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev,
> > >  	if (snaplen > res)
> > >  		snaplen = res;
> > >  
> > > -	if (atomic_read(&sk->sk_rmem_alloc) + skb->truesize >=
> > > -	    (unsigned)sk->sk_rcvbuf)
> > > +	if (atomic_read(&sk->sk_rmem_alloc) >= (unsigned)sk->sk_rcvbuf)
> > >  		goto drop_n_acct;
> > >  
> > >  	if (skb_shared(skb)) {
> > > @@ -1763,7 +1762,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
> > >  	if (po->tp_version <= TPACKET_V2) {
> > >  		if (macoff + snaplen > po->rx_ring.frame_size) {
> > >  			if (po->copy_thresh &&
> > > -				atomic_read(&sk->sk_rmem_alloc) + skb->truesize
> > > +				atomic_read(&sk->sk_rmem_alloc)
> > >  				< (unsigned)sk->sk_rcvbuf) {
> > >  				if (skb_shared(skb)) {
> > >  					copy_skb = skb_clone(skb, GFP_ATOMIC);
> > > 
> > > 
> > > 
> > > 
> > 
> > It doesn't work too.
> > It is possible to see this behavior on qemu. What about if I prepare you package with cross toolchain, rootfs
> > and you can add debug message where you want?
> > 
> > I have also tried ll_temac driver with ppc440 and behavior is the same.
> > 
> > Max FRAME_SIZE pass to netdev_alloc_skb_ip_align is 7966. For this value ping works.
> > (For ll_temac driver it is #define XTE_JUMBO_MTU 7948 from ll_temac.h)
> 
> I did several tests with MTU 9000 on my machines and it works well.
> 
> It seems my pings (iputils-sss20071127 or iputils-sss20101006) uses a
> big enough RCVBUF
> 
> setsockopt(3, SOL_SOCKET, SO_RCVBUF, [65536], 4) = 0
> getsockopt(3, SOL_SOCKET, SO_RCVBUF, [131072], [4]) = 0
> 
> Could you check with "strace ping..." what is doing busybox ?

I found it : Its too small for jumbo frames.

setsockopt(3, SOL_SOCKET, SO_RCVBUF, [7280], 4) = 0

networking/ping.c


        /* set recv buf (needed if we can get lots of responses: flood ping,
         * broadcast ping etc) */
        sockopt = (datalen * 2) + 7 * 1024; /* giving it a bit of extra room */
        setsockopt(pingsock, SOL_SOCKET, SO_RCVBUF, &sockopt, sizeof(sockopt));



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