linux-kernel - Re: [PATCH] i386-pda UP optimization

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Message-Id: <200611151858.09958.dada1@cosmosbay.com>
Date:	Wed, 15 Nov 2006 18:58:09 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andi Kleen <ak@...e.de>, akpm@...l.org,
	Arjan van de Ven <arjan@...radead.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i386-pda UP optimization

On Wednesday 15 November 2006 18:49, Ingo Molnar wrote:
> * Eric Dumazet <dada1@...mosbay.com> wrote:
> > Machine boots but freeze when init starts. Any idea ?
>
> probably caused by this:
> > +# define GET_CPU_NUM(reg)
> >
> >  #define FIXUP_ESPFIX_STACK \
> >  	/* since we are on a wrong stack, we cant make it a C code :( */ \
> > -	movl %gs:PDA_cpu, %ebx; \
> > +	GET_CPU_NUM(%ebx) \
> >  	PER_CPU(cpu_gdt_descr, %ebx); \
> >  	movl GDS_address(%ebx), %ebx; \
>
> %ebx very definitely wants to have a current CPU number loaded ;) Pick
> it up from the task struct.

Hum.... Are you sure ?

For UP we have this PER_CPU definition :

#define PER_CPU(var, cpu) \
        movl $per_cpu__/**/var, cpu;

You can see 'cpu' is a pure output , not an input value.

So I basically deleted the fist instruction of this sequence :

movl %gs:PDA_cpu, %ebx
movl $per_cpu__cpu_gdt_descr, %ebx;

Did I miss something ?
-
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