Message-ID: <1505557061.16316.7.camel@perches.com>
Subject: Re: [PATCH V2] tipc: Use bsearch library function
From: Joe Perches <joe@perches.com>
To: Ying Xue <ying.xue@windriver.com>, Thomas Meyer <thomas@m3y3r.de>,
        jon.maloy@ericsson.com, netdev@vger.kernel.org,
        tipc-discussion@lists.sourceforge.net, linux-kernel@vger.kernel.org,
        davem@davemloft.net
Date: Sat, 16 Sep 2017 03:17:41 -0700
In-Reply-To: <35f41984-22e9-5adc-0e4d-a4ef4204f6d7@windriver.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>
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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.