RE: [PATCH RFC] [x86] Optimize copy-page by reducing impact from HWprefetch

[Ma, Ling]

Forget to append experiment data:

1. We copy 4096 bytes for 32 times on snb, and extract minimum execution time 
On hot cache case: 
  Copy_page          copy_page_c 
  482 cycles          350 cycles

2. the same routine with hot-caches, but before each execution we copy 512k data to push original data out of L1 &L2.
On cold cache case:
  copy_page(with prefetch)    copy_page(without prefetch)      copy_page_c
   853~873 cycles                  1037~1051 cycles            959~976 cycles 

Thanks
Ling

> -----Original Message-----
> From: Ma, Ling
> Sent: Tuesday, June 28, 2011 11:24 PM
> To: 'Ingo Molnar'; Andi Kleen
> Cc: hpa@xxxxxxxxx; tglx@xxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: RE: [PATCH RFC] [x86] Optimize copy-page by reducing impact
> from HW prefetch
> 
> Hi Ingo
> 
> > Ling, mind double checking which one is the faster/better one on SNB,
> > in cold-cache and hot-cache situations, copy_page or copy_page_c?
> Copy_page_c
> on hot-cache copy_page_c on SNB combines data to 128bit (processor
> limit 128bit/cycle for write) after startup latency
> so it is faster than copy_page which provides 64bit/cycle for write.
> 
> on cold-cache copy_page_c doesn't use prefetch, which uses prfetch
> according to copy size,
> so copy_page function is better.
> 
> Thanks
> Ling

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