linux-kernel - Re: linux-next: build warnings after merge of the akpm tree

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Message-ID: <1351230291.12511.7.camel@wall-e>
Date:	Fri, 26 Oct 2012 07:44:51 +0200
From:	Stefani Seibold <stefani@...bold.net>
To:	Richard Yang <weiyang@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	richard -rw- weinberger <richard.weinberger@...il.com>,
	Jiri Kosina <jkosina@...e.cz>
Subject: Re: linux-next: build warnings after merge of the akpm tree

Am Freitag, den 26.10.2012, 06:36 +0800 schrieb Richard Yang:

> >
> >And holy cow that code is hard to read :( Why was kfifo_in()
> >implemented as a macro, anyway?  AFAICT all its args have a known type,
> >so we could have used a proper C interface, which would have fixed all
> >this nicely.
> 

Thats simple for performance reasons, the compiler remove most of the
code during the compile stage, so no runtime checks are necessary. And
it is the only way since C does not provides templates like C++.
 
> Hmm, move the definition of kfifo_in()/kfifo_out() into the kfifo.c?
> 

Don't do it. this will result in a performance degradation. Look at the
disassembled code by each change in code and compare it with the
previous one. I don't believe that you can produce better code.

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