netdev - Re: Packet time delays on multi-core systems

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Message-ID: <1285850812.2615.432.camel@edumazet-laptop>
Date:	Thu, 30 Sep 2010 14:46:52 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexey Vlasov <renton@...ton.name>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: Packet time delays on multi-core systems

Le jeudi 30 septembre 2010 à 16:30 +0400, Alexey Vlasov a écrit :
> On Wed, Sep 29, 2010 at 11:45:21PM +0200, Eric Dumazet wrote:
> > 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...
> 
> Yes, it's clear that  some slow down can appear, but 100 ms is too much,
> and this happens at 200 SYN packets in 2 minutes just as in my example.
> On old servers where some tx/rx are missing in NIC card I don't see
> such a situation even at more then 1000 SYN-packets per sec.

Because all cpus were servicing interrupts, which was good for your
needs. Things apparently changed with 2.6.32. 

You have a multiqueue NIC, but using a single CPU to handle the
workload.

> 
> > Is using other rules gives same problem ?
> >
> > iptables -A OUTPUT -p tcp -m tcp --dport 80 --tcp-flags
> 
> No, only LOG gives such a scheme.
> 


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