From mboxrd@z Thu Jan  1 00:00:00 1970
From: raimue@codingfarm.de (=?windows-1252?Q?Rainer_M=FCller?=)
Date: Wed, 20 Feb 2013 22:18:16 +0100
Subject: cpu_relax(), rep: nop, and PAUSE
In-Reply-To: <CAJJAcocc9FbgAUjRED_0iLt=iz58CrZf=hmSKZf91XANz+cgJw@mail.gmail.com>
References: <CAJJAcocc9FbgAUjRED_0iLt=iz58CrZf=hmSKZf91XANz+cgJw@mail.gmail.com>
Message-ID: <kg3eik$ank$1@ger.gmane.org>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

On 2013-02-19 13:20, David Shwatrz wrote:
> We have:
> #define cpu_relax()	asm volatile("rep; nop")
> in arch/x86/boot/boot.h.
> 
> Why don't we use the PAUSE assembler instruction here ?

If you dig further into the Intel x86 manual, the machine instructions
'pause' and 'rep;nop' actually use the exact same encoding. As some
older assembler might not know the 'pause' mnemonic, using 'rep;nop'
here is most probably for backwards compatibility.

Rainer