From: Jamie Lokier <lk@tantalophile.demon.co.uk>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Jean-Marc Saffroy <saffroy@ri.silicomp.fr>,
linux-kernel@vger.kernel.org, linux-smp@vger.kernel.org
Subject: Re: [Q] Implementation of spin_lock on i386: why "rep;nop" ?
Date: Wed, 19 Sep 2001 04:42:03 +0100 [thread overview]
Message-ID: <20010919044203.A20143@kushida.degree2.com> (raw)
In-Reply-To: <Pine.LNX.4.31.0109171725140.26090-100000@sisley.ri.silicomp.fr> <E15j2BM-0007WU-00@the-village.bc.nu>
In-Reply-To: <E15j2BM-0007WU-00@the-village.bc.nu>; from alan@lxorguk.ukuu.org.uk on Mon, Sep 17, 2001 at 06:27:44PM +0100
Alan Cox wrote:
> > The "rep;nop" line looks dubious, since the IA-32 programmer's manual from
> > Intel (year 2001) mentions that the behaviour of REP is undefined when it
> > is not used with string opcodes. BTW, according to the same manual, REP is
> > supposed to modify ecx, but it looks like is is not the case here... which
> > is fortunate, since ecx is never saved. :-)
>
> rep nop is a pentium IV operation. Its retroactively after testing defined
> to be portable and ok.
Are we sure that the value of ECX doesn't matter on a 386? Or does it
count down doing nops ECX times on a 386?
-- Jamie
next prev parent reply other threads:[~2001-09-19 3:42 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-09-17 16:16 [Q] Implementation of spin_lock on i386: why "rep;nop" ? Jean-Marc Saffroy
2001-09-17 16:22 ` Dave Jones
2001-09-17 17:19 ` Jean-Marc Saffroy
2001-09-17 16:42 ` Richard B. Johnson
2001-09-17 17:06 ` Jonathan Lundell
2001-09-17 17:27 ` Alan Cox
2001-09-17 19:47 ` H. Peter Anvin
2001-09-19 3:42 ` Jamie Lokier [this message]
2001-09-19 4:06 ` Brian Gerst
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