linux-kernel - Re: [PATCH 18/23] sparc: use the new byteorder headers

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Date:	Tue, 19 Aug 2008 01:43:50 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	harvey.harrison@...il.com
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 18/23] sparc: use the new byteorder headers

From: Harvey Harrison <harvey.harrison@...il.com>
Date: Mon, 18 Aug 2008 17:48:17 -0700

> Signed-off-by: Harvey Harrison <harvey.harrison@...il.com>

I'm not so sure about this.

If I understand the ___swab*() inlines in linux/swab.h,
it has the following priority of swapping methods:

1) If arch defines __arch_swab*(), this is used.

2) If arch defines __arch_swab*p(), variable is popped onto
   the stack and we do the pointer based operation.

3) Else normal C version is used.

Case #2 is totally disagree with.

Especially for small swaps such as 16-bit the inline expansion
of the portable C code is going to be much better than popping
the variable onto and then back off the stack.

Sparc 64-bit only provides the __arch_swab*p() routines so
#2 is what will in fact be used here.

So NACK based upon that analysis.
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