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SubjectRe: [PATCH] task_struct colouring ...
On 30 Nov 2001, H. Peter Anvin wrote:

> Followup to: <>
> By author: Davide Libenzi <>
> In newsgroup:
> >
> > The point is why store kernel pointers in global registers when You can
> > achieve the same functionality, with a smaller patch, that does not need
> > to be recoded for each CPU, without using global registers.
> >
> Because global registers are faster! This is exactly the kind of
> stuff that is properly CPU-dependent and should be treated as such.
> Heck, it even depends on what kind of multiprocessor architecture, if
> any, you're using!
> That being said, I belive that on most, if not all, processors, the
> idea of having the pointer point not to "current" but to a per-CPU
> memory area is *very* appealing, and a change that should be made
> uniform unless it's a significant lose on some machines...

Again this is the "current" diff :

static inline struct task_struct * get_current(void)
- struct task_struct *current;
- __asm__("andl %%esp,%0; ":"=r" (current) : "0" (~8191UL));
- return current;
+ unsigned long *tskptr;
+ __asm__("andl %%esp,%0; ":"=r" (tskptr) : "0" (~8191UL));
+ return (struct task_struct *) *tskptr;

that will probably resolve in something like:

movl %esp, %eax
andl $-8192, %eax
movl (%eax), %eax

- Davide

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