From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Monjalon <thomas.monjalon-pdR9zngts4EAvxtiuMwx3w@public.gmane.org>
Subject: Re: [memnic PATCH v2 6/7] pmd: add branch hint in
	recv/xmit
Date: Tue, 30 Sep 2014 16:51:10 +0200
Message-ID: <5360316.uoHmy6EYU1@xps13>
References: <7F861DC0615E0C47A872E6F3C5FCDDBD02AE26C5@BPXM14GP.gisp.nec.co.jp>
 <C37D651A908B024F974696C65296B57B0F2B03A9@SHSMSX101.ccr.corp.intel.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7Bit
Cc: dev-VfR2kkLFssw@public.gmane.org, Hayato Momma <h-momma-JhyGz2TFV9J8UrSeD/g0lQ@public.gmane.org>
To: "Xie, Huawei" <huawei.xie-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Return-path: <dev-bounces-VfR2kkLFssw@public.gmane.org>
In-Reply-To: <C37D651A908B024F974696C65296B57B0F2B03A9-0J0gbvR4kThpB2pF5aRoyrfspsVTdybXVpNB7YpNyf8@public.gmane.org>
List-Id: patches and discussions about DPDK <dev.dpdk.org>
List-Unsubscribe: <http://dpdk.org/ml/options/dev>,
 <mailto:dev-request-VfR2kkLFssw@public.gmane.org?subject=unsubscribe>
List-Archive: <http://dpdk.org/ml/archives/dev/>
List-Post: <mailto:dev-VfR2kkLFssw@public.gmane.org>
List-Help: <mailto:dev-request-VfR2kkLFssw@public.gmane.org?subject=help>
List-Subscribe: <http://dpdk.org/ml/listinfo/dev>,
 <mailto:dev-request-VfR2kkLFssw@public.gmane.org?subject=subscribe>
Errors-To: dev-bounces-VfR2kkLFssw@public.gmane.org
Sender: "dev" <dev-bounces-VfR2kkLFssw@public.gmane.org>

2014-09-30 14:38, Xie, Huawei:
> > -		if (++next >= MEMNIC_NR_PACKET)
> > +		if (unlikely(++next >= MEMNIC_NR_PACKET))
> 
> On IA,  compiler can use add, cmp and cmov to avoid branch.
> But If MEMNIC_NR_PACKET is always power of 2, 
> 	it is better just next = (next + 1) & (MEMNIC_NR_PACKET - 1)

Power of 2 is not enforced for MEMNIC_NR_PACKET.

-- 
Thomas