From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <pullururajasekhar@gmail.com>
Received: from mail-ie0-f175.google.com (mail-ie0-f175.google.com
 [209.85.223.175]) by dpdk.org (Postfix) with ESMTP id C275C6849
 for <dev@dpdk.org>; Tue, 31 Mar 2015 17:13:19 +0200 (CEST)
Received: by iedm5 with SMTP id m5so18500114ied.3
 for <dev@dpdk.org>; Tue, 31 Mar 2015 08:13:19 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113;
 h=mime-version:date:message-id:subject:from:to:cc:content-type;
 bh=cJoE/oVkjG2dqEe33aKe+GxSt654weSbeUAURS7OhXM=;
 b=VZ4KsAwfjJ/H2MaSUz1bNnK2tEojsgyFwea1lyu2LPz0NpzXeiN9Hal9EvcdllyXXv
 X4vqc+/UhD2mEu4OfLib52CFuDJ4hDgm47X4eYloX4roL9jVxVFT4mgT2c5FwYSLokWg
 ag0RRdxqlhCBKXFoCDFj4+svqBeUa4vEusxAIUqssulWLeUXnMTnfx5vXi4w6c6xE2Gl
 0O+J1QlwYPpG6V3xjzEtXY2zs4YPgO+P8GFA32WIDuqcaUWAel32MdSF4PQ371odlnWQ
 DH+Fm1wQab6hnHbvaPa/ietQjul69gWywV7gxiclyXL1mB/6lzIM6fWdg4bLhr3twGT+
 WJtw==
MIME-Version: 1.0
X-Received: by 10.107.133.16 with SMTP id h16mr56337808iod.31.1427814799108;
 Tue, 31 Mar 2015 08:13:19 -0700 (PDT)
Received: by 10.50.182.232 with HTTP; Tue, 31 Mar 2015 08:13:19 -0700 (PDT)
Date: Tue, 31 Mar 2015 20:43:19 +0530
Message-ID: <CAGA5_H7vifeV=8Rtvd8M0VPWzz70xQPcZ8v4ND7+GG=15-_qkw@mail.gmail.com>
From: Rajasekhar Pulluru <pullururajasekhar@gmail.com>
To: dev@dpdk.org
Content-Type: text/plain; charset=UTF-8
Subject: [dpdk-dev] Queries on dpdk buffer allocation and kni
X-BeenThere: dev@dpdk.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: patches and discussions about DPDK <dev.dpdk.org>
List-Unsubscribe: <http://dpdk.org/ml/options/dev>,
 <mailto:dev-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://dpdk.org/ml/archives/dev/>
List-Post: <mailto:dev@dpdk.org>
List-Help: <mailto:dev-request@dpdk.org?subject=help>
List-Subscribe: <http://dpdk.org/ml/listinfo/dev>,
 <mailto:dev-request@dpdk.org?subject=subscribe>
X-List-Received-Date: Tue, 31 Mar 2015 15:13:20 -0000

Dear Group members,

I have been trying to understand the dpdk code and have got two queries.

1. descriptor rings and packet buffer allocation

Looking at the linux native e1000 kernel driver,
Memory for NIC's tx and rx descriptor rings are allocated using
dma_alloc_coherent.
Memory for rx packet buffers are allocated using netdev_alloc_skb and
dma address (after dma_map_single) of skb->data is set to rx
descriptor to receive packet onto skb.

Looking at dpdk user space driver, all rings and packet allocation is
done using (dpdk) mem pools.

I would like to know

a) whether the mem pool internally uses dma_alloc_coherent like apis
to allocate buffers
b) if the buffer is allocated by kernel, how does the user space
application map them and access the packet data directly.

2. kni

what is the internal mechanism used to implement FIFO-based shared
memory (used between kernel and user-land).

Thanks in advance,
Rajasekhar