Re: Change ia64 prefetch to use lfetch.fault

From: david mosberger <dmosberger_at_gmail.com>
Date: 2005-07-29 11:58:36
No, it doesn't --- it actually hurt performance last time I measured
it.  Basically, Linux uses prefetch() too often with bad/NULL
pointers, IIRC.  Check my earlier mails where I fixed the IVT code to
properly handle lfetch.fault (from a couple of months ago).

  --david

On 7/28/05, Chen, Kenneth W <kenneth.w.chen@intel.com> wrote:
> I don't remember whether this has been discussed earlier, won't
> it make sense to use the fault variant of lfetch for prefetch()
> and prefetchw()?  After all, the caller has high confidence that
> the cache line will be used in the future.
> 
> 
> Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
> 
> --- linux-2.6.12/include/asm-ia64/processor.h.orig      2005-07-28 14:46:26.629519713 -0700
> +++ linux-2.6.12/include/asm-ia64/processor.h   2005-07-28 14:48:17.037721485 -0700
> @@ -682,13 +682,13 @@ ia64_imva (void *addr)
>  static inline void
>  prefetch (const void *x)
>  {
> -        ia64_lfetch(ia64_lfhint_none, x);
> +       ia64_lfetch_fault(ia64_lfhint_none, x);
>  }
> 
>  static inline void
>  prefetchw (const void *x)
>  {
> -       ia64_lfetch_excl(ia64_lfhint_none, x);
> +       ia64_lfetch_fault_excl(ia64_lfhint_none, x);
>  }
> 
>  #define spin_lock_prefetch(x)  prefetchw(x)
> 
> -
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-- 
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Received on Thu Jul 28 21:58:58 2005

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