Re: [RFC Patch]Use ar.kr2 for smp_processor_id

From: Zou Nan hai <nanhai.zou_at_intel.com>
Date: 2007-02-08 15:27:31
On Thu, 2007-02-08 at 14:04, Keith Owens wrote:
> Zou Nan hai (on 08 Feb 2007 11:28:44 +0800) wrote:
> >Pin ar.kr2 of each CPU, so that smp_processor_id can use it.
> 
> Historically ar.k2 has been reserved for debugging purposes, for
> example in ivt.S.  Debuggers often need a location that can be used to
> track progress, it has to be somewhere that does not rely on TLB
> entries and is guaranteed to appear in MCA/INIT records - ar.k2 is
> perfect for this.
> 
  Ok, seems that current kr3 is only used by ia64_itc_printk_clock?
> Use Tony's suggestion of testing for a change in ar.k3 (guaranteed to
> be unique on every cpu) and caching the corresponding cpu number when
> it changes.
> 
  But why do we even need to cache it? 

  It is already in a register if we put it to kr3. 
  so smp_processor_id() could be very fast. and later sys_getcpu can
also be very fast.
 

  Thanks
  Zou Nan hai
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Received on Thu Feb 08 17:22:39 2007

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