linux-kernel - Re: [PATCH] fix vmstat per cpu usage

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Date:	Wed, 2 Aug 2006 11:01:22 +0200
From:	Jan Blunck <jblunck@...e.de>
To:	Andrew Morton <akpm@...l.org>
Cc:	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH] fix vmstat per cpu usage

On Tue, Aug 01, Andrew Morton wrote:

> >  
> >  static inline void __count_vm_event(enum vm_event_item item)
> >  {
> > -	__get_cpu_var(vm_event_states.event[item])++;
> > +	__get_cpu_var(vm_event_states).event[item]++;
> >  }
> 
> How odd.  Are there any negative consequences to the existing code?

In asm-s390/percpu.h we use

 #define __get_cpu_var(var) __reloc_hide(var,S390_lowcore.percpu_offset)

and for modules on s390x __reloc_hide() is defined as

 #define __reloc_hide(var,offset) \
   (*({ unsigned long *__ptr; \
        asm ( "larl %0,per_cpu__"#var"@GOTENT" \
              : "=a" (__ptr) : "X" (per_cpu__##var) ); \
        (typeof(&per_cpu__##var))((*__ptr) + (offset)); }))

which leads in this case to

 larl %0, per_cpu__vm_event_states.event[item]@GOTENT

which is invalid asm.
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