netdev - Re: [BUG,REGRESSION?] 3.11.6+,3.12: GbE iface rate drops to few KB/s

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Date:	Tue, 19 Nov 2013 16:43:48 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Willy Tarreau <w@....eu>
Cc:	Arnaud Ebalard <arno@...isbad.org>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	simon.guinot@...uanux.org, netdev@...r.kernel.org,
	edumazet@...gle.com, Cong Wang <xiyou.wangcong@...il.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [BUG,REGRESSION?] 3.11.6+,3.12: GbE iface rate drops to few KB/s

On Wed, 2013-11-20 at 01:35 +0100, Willy Tarreau wrote:
> On Tue, Nov 19, 2013 at 04:08:49PM -0800, Eric Dumazet wrote:
> > On Wed, 2013-11-20 at 00:53 +0100, Arnaud Ebalard wrote:
> > 
> > > Anyway, I think if the thread keeps going on improving mvneta, I'll do
> > > all additional tests from RAM and will stop polluting netdev w/ possible
> > > sata/disk/fs issues.
> > 
> > ;)
> > 
> > Alternative would be to use netperf or iperf to not use disk at all
> > and focus on TCP/network issues only.
> 
> Yes, that's for the same reason that I continue to use inject/httpterm
> for such purposes :
>   - httpterm uses tee()+splice() to send pre-built pages without copying ;
>   - inject uses recv(MSG_TRUNC) to ack everything without copying.
> 
> Both of them are really interesting to test the hardware's capabilities
> and to push components in the middle to their limits without causing too
> much burden to the end points.
> 
> I don't know if either netperf or iperf can make use of this now, and
> I've been used to my tools, but I should take a look again.

netperf -t TCP_SENDFILE  does the zero copy at sender.

And more generally -V option does copy avoidance

(Use splice(sockfd -> nullfd) at receiver if I remember well)


Anyway, we should do the normal copy, because it might demonstrate
scheduling problems.

If you want to test raw speed, you could use pktgen ;)



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