Messages in this thread | | | Date | Fri, 30 Nov 2001 17:30:19 -0800 (PST) | From | Davide Libenzi <> | Subject | Re: [PATCH] task_struct colouring ... |
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On 30 Nov 2001, H. Peter Anvin wrote:
> Followup to: <Pine.LNX.4.40.0111301614000.1600-100000@blue1.dev.mcafeelabs.com> > By author: Davide Libenzi <davidel@xmailserver.org> > In newsgroup: linux.dev.kernel > > > > 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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