netdev - Re: Packet mmap: TX RING and zero copy

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Message-ID: <7e63f56c0809050328j63b901dbgffb0fa5836229d70@mail.gmail.com>
Date:	Fri, 5 Sep 2008 13:28:03 +0300
From:	"Robert Iakobashvili" <coroberti@...il.com>
To:	"Johann Baudy" <johaahn@...il.com>
Cc:	netdev@...r.kernel.org,
	"Ulisses Alonso Camaró" <uaca@...mni.uv.es>
Subject: Re: Packet mmap: TX RING and zero copy

Hi Johann,

On Tue, Sep 2, 2008 at 9:27 PM, Johann Baudy <johaahn@...il.com> wrote:
> I've made lot of tests, playing with jumbo frames, raw sockets, ...
> I've never exceeded ~25Mbytes/s. So I've decided to analyze deeply the
> packet socket transmission process.
>
> The main blocking point was the memcpy_fromiovec() function that is
> located in the packet_sendmsg() of af_packet.c.
> It was consuming all my CPU resources to copy data from user space to
> socket buffer.
> Then I've started to work on a hack that makes this transfer possible
> without any memcpys.
>
> Mainly, the hack is the implementation of two "features":
>
>    *  Sending packet through a circular buffer between user and
> kernel space that minimizes the number of system calls. (Feature
> actually implemented for capture process, libpcap ..).

Something like this has been done in PF_RING socket,
which is a part of ntop project infra.

Take care.

Truly,
Robert Iakobashvili
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