From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <thomas.monjalon@6wind.com>
Received: from mail-wi0-f171.google.com (mail-wi0-f171.google.com
 [209.85.212.171]) by dpdk.org (Postfix) with ESMTP id 541BBDE6
 for <dev@dpdk.org>; Wed, 22 Jul 2015 10:56:23 +0200 (CEST)
Received: by wicgb10 with SMTP id gb10so88112663wic.1
 for <dev@dpdk.org>; Wed, 22 Jul 2015 01:56:23 -0700 (PDT)
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
 d=1e100.net; s=20130820;
 h=x-gm-message-state:from:to:cc:subject:date:message-id:organization
 :user-agent:in-reply-to:references:mime-version
 :content-transfer-encoding:content-type;
 bh=aYMaVuRxbBlkVe1mfvMIpvG/E9DhrpISLdiqeXU37xQ=;
 b=E1eRLRh91IBbd1y0zQj3lUaDju/ukh28/uQ6jvGBRwZZS9+7KZlnvDMX1LgDO+KTUg
 eRChuTDo2ZIGi830VhESCuNt7KbxP10pPgYr+mWXetF1ukyGpHJhM422wukjOCtwDp+k
 /FThXIrln8MI3UXuKjH1oAt94AGirS1l3thHwfffQfcG2Da6XwRBIFwkb3YMOV1mzkTv
 8qjwFN2Js8OA/P2Vlwhkwm4VZd7n/HwIPUW9CtjrgDNIdTYESsTok+JWY3RfJ7GjdGiX
 Dlp16TJjnRinkgLxFMwT9fZ7/lnjwYhQUKCfJWTIjKHmP8AZHZNZIDyXPzQJ250jH4og
 nCTw==
X-Gm-Message-State: ALoCoQlK9rgeJ8OI8mfHMtziKoug4Y88f9MBHpvT+E0QaQxg0rz/4zg9ph8uZPOv/leHpLXzMleQ
X-Received: by 10.180.99.168 with SMTP id er8mr4307730wib.86.1437555383149;
 Wed, 22 Jul 2015 01:56:23 -0700 (PDT)
Received: from xps13.localnet (136-92-190-109.dsl.ovh.fr. [109.190.92.136])
 by smtp.gmail.com with ESMTPSA id r8sm15630978wiz.5.2015.07.22.01.56.21
 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
 Wed, 22 Jul 2015 01:56:22 -0700 (PDT)
From: Thomas Monjalon <thomas.monjalon@6wind.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Date: Wed, 22 Jul 2015 10:55:11 +0200
Message-ID: <79868347.qM8YWBKqTE@xps13>
Organization: 6WIND
User-Agent: KMail/4.14.8 (Linux/4.0.4-2-ARCH; KDE/4.14.8; x86_64; ; )
In-Reply-To: <1437417646-11221-2-git-send-email-stephen@networkplumber.org>
References: <1437417646-11221-1-git-send-email-stephen@networkplumber.org>
 <1437417646-11221-2-git-send-email-stephen@networkplumber.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 7Bit
Content-Type: text/plain; charset="us-ascii"
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH v2 1/2] virtio: fix queue size and number of
	descriptors
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: Wed, 22 Jul 2015 08:56:23 -0000

2015-07-20 11:40, Stephen Hemminger:
> The number of descriptors can be either zero to use the whole
> available ring, or some value smaller. This is used to limit
> the number of mbufs allocated for the receive ring. If more
> descriptors are requested than available the size is silently
> truncated.
[...]
> +	if (nb_desc == 0 || nb_desc > vq_size)
> +		nb_desc = vq_size;

This behaviour should be common to every drivers and explained in the API doxygen:
http://dpdk.org/browse/dpdk/tree/lib/librte_ether/rte_ethdev.h?id=v2.1.0-rc1#n1843