From: Jon Maloy <jon.maloy@ericsson.com>
To: Joe Perches <joe@perches.com>, Ying Xue <ying.xue@windriver.com>,
        "Thomas Meyer" <thomas@m3y3r.de>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "tipc-discussion@lists.sourceforge.net" 
        <tipc-discussion@lists.sourceforge.net>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "davem@davemloft.net" <davem@davemloft.net>
Subject: RE: [PATCH V2] tipc: Use bsearch library function
Thread-Topic: [PATCH V2] tipc: Use bsearch library function
Thread-Index: AQHTLsCFggJ6hPSP+EWhjy5rbdPPE6K3N4aAgAAGogCAAALngIAABiAAgAADfYCAAAHhgIAAMg2Q
Date: Sat, 16 Sep 2017 13:20:28 +0000
Message-ID: <DB5PR0701MB1958558286B3B455C601754A9A6D0@DB5PR0701MB1958.eurprd07.prod.outlook.com>
References: <20170911.143025.555018840006192902.davem@davemloft.net>
         <20170916075036.28676-1-thomas@m3y3r.de>
         <16128f5e-66ff-b6ec-c0e1-74ea08c212b0@windriver.com>
         <1505553970.16316.1.camel@perches.com>
         <64ee51ce-eb7e-ac1c-56a9-9481f6f80b35@windriver.com>
         <1505555908.16316.5.camel@perches.com>
         <35f41984-22e9-5adc-0e4d-a4ef4204f6d7@windriver.com>
 <1505557061.16316.7.camel@perches.com>
In-Reply-To: <1505557061.16316.7.camel@perches.com>
Accept-Language: en-US
Content-Language: en-US
spamdiagnosticoutput: 1:99
spamdiagnosticmetadata: NSPM
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-originalarrivaltime: 16 Sep 2017 13:20:28.6662
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 92e84ceb-fbfd-47ab-be52-080c6b87953f
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB5PR0701MB2008
X-OriginatorOrg: ericsson.com
X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFlrMKsWRmVeSWpSXmKPExsUyM2K7tK686t5Ig6fv+SzmnG9hsZh9/zGL
        xeVdc9gsji0Qs7i2YDqjxZbzWQ5sHltW3mTy2L3gM5PHvP+32Dy+rLrG7PF5k1wAaxSXTUpq
        TmZZapG+XQJXxoW//5gLnglVTG7naWB8xNfFyMkhIWAi8X7xDqYuRi4OIYEjjBINf+YygiSE
        BE4wShz7qAmSYBHoZZY4/OMqVNVcJonv/4+wQTjPGSX+HnwK1sImoCHxcloHI0hCROAek8TU
        LZuZQBLCAlYSm/eeYwOxRQSsJXp6DwEVcQDZURIf3gaDhFkEVCX+Lz/OAmLzCiRInNxwiwVi
        wX5mib2T/4PN4RQwllj5YRpYEaOAmMT3U2vA4swC4hK3nsxngnhIQGLJnvPMELaoxMvH/1hB
        djEKREqcfhoJEVaUOL9hEVSJrMSl+d2MEHYHu8TkqWEQtp7E1olvwc6UEPCVWHOVH+QcCYEn
        TBLtN5ugVulILL50BKrXRmJG93SomRUSW56cZIWw8yWWrvjIAtF8nlVi7bXpLBAJGYmDBxax
        T2DUnYXkBQhbR2LB7k9sELa2xLKFr5lngcNFUOLkzCcsCxhZVjGKFqcWJ+WmGxnrpRZlJhcX
        5+fp5aWWbGIEJp2DW36r7mC8/MbxEKMAB6MSD+82ub2RQqyJZcWVuYcYJTiYlUR4m1WAQrwp
        iZVVqUX58UWlOanFhxilOViUxHkd912IEBJITyxJzU5NLUgtgskycXBKNTDyLrNq8hZcGD1j
        Akdc+oSzbate7Hqet1PPSX3j1blx0RNvHOmv+Fa1VnhlUdGfr3OOmXEo3mdU0zo1ddLRRZ22
        kqcKOGMfTfhy6ugL3uLvNmE/f5nvmva0WntBM1eP8sfOywXprZ96l+U90hZhl33kHLGN7b7W
        p4THq60/v4p6pWob7HiVva9BiaU4I9FQi7moOBEAQIToFTYDAAA=
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Transfer-Encoding: 8bit
X-MIME-Autoconverted: from quoted-printable to 8bit by nfs id v8GDZfr2019807
Content-Length: 2337
Lines: 55


> -----Original Message-----
> From: netdev-owner@vger.kernel.org [mailto:netdev-
> owner@vger.kernel.org] On Behalf Of Joe Perches
> Sent: Saturday, September 16, 2017 06:18
> To: Ying Xue <ying.xue@windriver.com>; Thomas Meyer
> <thomas@m3y3r.de>; Jon Maloy <jon.maloy@ericsson.com>;
> netdev@vger.kernel.org; tipc-discussion@lists.sourceforge.net; linux-
> kernel@vger.kernel.org; davem@davemloft.net
> Subject: Re: [PATCH V2] tipc: Use bsearch library function
> 
> On Sat, 2017-09-16 at 18:10 +0800, Ying Xue wrote:
> > On 09/16/2017 05:58 PM, Joe Perches wrote:
> > > On Sat, 2017-09-16 at 17:36 +0800, Ying Xue wrote:
> > > > On 09/16/2017 05:26 PM, Joe Perches wrote:
> > > > > On Sat, 2017-09-16 at 17:02 +0800, Ying Xue wrote:
> > > > > > On 09/16/2017 03:50 PM, Thomas Meyer wrote:
> > > > > > > Use common library function rather than explicitly coding
> > > > > > > some variant of it yourself.
> > > > > > >
> > > > > > > Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
> > > > > >
> > > > > > Acked-by: Ying Xue <ying.xue@windriver.com>
> > > > >
> > > > > Are you sure you want to do this?
> > > > >
> > > > > Note the comment above nameseq_find_subseq
> > > > >
> > > > >  * Very time-critical, so binary searches through sub-sequence array.
> > > > >
> > > > > What impact does this change have on performance?
> > > >
> > > > Sorry, I couldn't see any essential difference between this new
> > > > implementation and the original one except that the former tries
> > > > to use the library function - bsearch() to replace the original
> > > > binary search algorithm implemented in TIPC itself. Therefore, I
> > > > don't think the change will have a big impact on performance.
> > > >
> > > > If I miss something, please let me know.
> > >
> > > Comparison via a function pointer in bsearch is slower than direct
> > > code without the function call overhead.
> > >
> >
> > Right, but probably we can tolerate the slight sacrifice here.
> 
> What part of "very time critical" have you verified and benchmarked as
> inconsequential?
> 
> Please post your results.

I agree with Joe here. This change does not simplify anything, it does not reduce the amount of code, plus that it introduce an unnecessary outline call in a place where we have every reason to let the compiler do its optimization job properly.

///jon