netdev - Re: [PATCH net-next 2/2] openvswitch: Use zerocopy if applicable when performing the upcall

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Message-ID: <20130525070222.GB30252@casper.infradead.org>
Date:	Sat, 25 May 2013 08:02:22 +0100
From:	Thomas Graf <tgraf@...g.ch>
To:	Jesse Gross <jesse@...ira.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	netdev <netdev@...r.kernel.org>,
	"dev@...nvswitch.org" <dev@...nvswitch.org>
Subject: Re: [PATCH net-next 2/2] openvswitch: Use zerocopy if applicable
 when performing the upcall

On 05/24/13 at 03:18pm, Jesse Gross wrote:
> On Fri, May 24, 2013 at 2:57 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> >> My guess is that there isn't a real different for small packets since
> >> everything will be in the cache but it seems worth checking given that
> >> this is optimizing a rare case at the expense of the common one.
> >
> > I really doubt checksumming a SYN/ACK packet is that a performance
> > issue. Do you have performance numbers ?
> >
> > You could always provide a patch to restore this copy/checksum if it
> > really gives a benefit, and if people still use NIC not doing this
> > checksum.
> 
> If it makes a difference then it needs to be addressed before this
> patch goes in since it's the common case. I don't think it will but
> that's why I'm asking for numbers.

I ran TCP_CRR to verify the SYN/ACK use case and I did not
observe a difference. If you have any specific test in mind
I will be glad to run that before posting the 2nd revision.

The CPU numbers as reported was seen when testing with pktgen
at 1400 bytes with 8K flows and a 10/8 random IP source address.
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