linux-kernel - Re: Packet time delays on multi-core systems

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Message-ID: <20100930062419.GD86786@beaver.vrungel.ru>
Date:	Thu, 30 Sep 2010 10:24:19 +0400
From:	Alexey Vlasov <renton@...ton.name>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: Packet time delays on multi-core systems

Here I found some dude with the same problem:
http://lkml.org/lkml/2010/7/9/340

On Wed, Sep 29, 2010 at 11:45:21PM +0200, Eric Dumazet wrote:
> Le mercredi 29 septembre 2010 ?? 23:18 +0400, Alexey Vlasov a ??crit : 
> > Hi.
> > 
> > I'm not sure actually that I should write here, may be I should ask in
> > netfilter maillist, but if is something wrong please correct me.
> > 
> 
> CC netdev
> 
> 
> > I've got rather large linux shared hosting, and on my new servers I
> > noticed some strange singularity, that this simple rule:
> > 
> > # iptables -A OUTPUT -p tcp -m tcp --dport 80 --tcp-flags
> > FIN,SYN,RST,ACK SYN -j LOG --log-prefix "ipsec:SYN-OUTPUT "
> > --log-uid
> > 
> > gives essential time delays simply at ping from the adjacent server
> > on a local area network. I don't know precisely what's wrong whether the
> > reason is in the bad support by a kernel of new hardware, or it concerns
> > generally the new kernel, but now it leads to the situation that even at simple
> > DDOS attacks to client sites, it becomes difficult to make something, and in
> > general all works only worse.
> > 
> > It seems to me that with the increase of CPU cores' amount, it only becomes
> > worse and worse, and, obviously, iptables uses resources of only one processor,
> > which resources to it for any reason doesn't suffice.
> > 
> 
> Its not true. iptables can run on all cpus in //
> 
> > newbox # iptables -F
> > otherbox # ping -c 100 newbox
> > ...
> > 100 packets transmitted, 100 received, 0% packet loss, time 100044ms
> > rtt min/avg/max/mdev = 0.133/2.637/17.172/3.736 ms
> > 
> > OK.
> > 
> > newbox # iptables -A OUTPUT -p tcp -m tcp --dport 80 --tcp-flags FIN,SYN,RST,ACK SYN
> > -j LOG --log-prefix "ipsec:SYN-OUTPUT " --log-uid
> > otherbox # ping -c 100 newbox
> > ...
> > 64 bytes from (newbox): icmp_seq=3 ttl=64 time=1.58 ms
> > 64 bytes from (newbox): icmp_seq=4 ttl=64 time=98.7 ms
> > 64 bytes from (newbox): icmp_seq=5 ttl=64 time=18.2 ms
> > 64 bytes from (newbox): icmp_seq=6 ttl=64 time=6.13 ms
> > 64 bytes from (newbox): icmp_seq=7 ttl=64 time=108 ms
> > ...
> > 64 bytes from (newbox): icmp_seq=55 ttl=64 time=2.30 ms
> > 64 bytes from (newbox): icmp_seq=56 ttl=64 time=59.9 ms
> > 64 bytes from (newbox): icmp_seq=57 ttl=64 time=0.155 ms
> > ...
> > 64 bytes from (newbox): icmp_seq=61 ttl=64 time=13.4 ms
> > 64 bytes from (newbox): icmp_seq=62 ttl=64 time=55.0 ms
> > 64 bytes from (newbox): icmp_seq=63 ttl=64 time=0.233 ms
> > ...
> > 100 packets transmitted, 100 received, 0% packet loss, time 99957ms
> > rtt min/avg/max/mdev = 0.111/7.519/108.061/18.478 ms
> > 
> > newbox # iptables -L -v -n
> > Chain INPUT (policy ACCEPT 346K packets, 213M bytes)
> >  pkts bytes target     prot opt in     out     source               destination
> > 
> > Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
> >  pkts bytes target     prot opt in     out     source               destination
> > 
> > Chain OUTPUT (policy ACCEPT 296K packets, 290M bytes)
> >  pkts bytes target     prot opt in     out     source               destination
> >   234 14040 LOG        tcp  --  *      *       0.0.0.0/0            0.0.0.0/0    
> > tcp dpt:80 flags:0x17/0x02 LOG flags 8 level 4 prefix `ipsec:SYN-OUTPUT- '
> > 
> > My old server: Intel SR1500, Xeon 5430, kernel 2.6.24 - 2.6.28
> > Newbox: SR1620UR, 5650, kernel 2.6.32
> > 
> > Thanks in advance.
> > 
> 
> Seems strange indeed, since the LOG you add should not slowdown icmp
> trafic that much.
> 
> But if you send SYN packets in the same time, (logged), this might slow
> down the reception (and answers) of ICMP frames. LOG target can be quite
> expensive... 
> 
> Is using other rules gives same problem ?
> 
> iptables -A OUTPUT -p tcp -m tcp --dport 80 --tcp-flags FIN,SYN,RST,ACK SYN
> iptables -A OUTPUT -p tcp -m tcp --dport 80 --tcp-flags FIN,SYN,RST,ACK SYN
> iptables -A OUTPUT -p tcp -m tcp --dport 80 --tcp-flags FIN,SYN,RST,ACK SYN
> iptables -A OUTPUT -p tcp -m tcp --dport 80 --tcp-flags FIN,SYN,RST,ACK SYN
> 
> 
> 
> 
> 
> --
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-- 
BRGDS. Alexey Vlasov.
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