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Date: Thu, 22 Jan 2015 11:34:27 +0000
From: Bruce Richardson <bruce.richardson@intel.com>
To: Tetsuya Mukawa <mukawa@igel.co.jp>
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Subject: Re: [dpdk-dev] some questions about  rte_memcpy
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On Thu, Jan 22, 2015 at 07:23:49PM +0900, Tetsuya Mukawa wrote:
> On 2015/01/22 16:35, Matthew Hall wrote:
> > On Thu, Jan 22, 2015 at 01:32:04PM +0800, Linhaifeng wrote:
> >> Do you mean if call rte_memcpy before rte_eal_init() would crash?why?
> > No guarantee. But a theory. It might use some things from the EAL init to 
> > figure out which version of the accelerated algorithm to use.
> 
> This selection is done at compile-time.
> And if the size is constant, I guess DPDK assumes memcpy is replaced by
> inline __builtin_memcpy.
> I haven't checked the performance of builtin memcpy, but probably much
> faster.
> 

Yes, that assumption is correct. A couple of years ago we discovered that for
constant size values, the compiler would generate much faster code for us
using a regular memcpy than rte_memcpy, hence the macro.

/Bruce

> Tetsuya
> 
> > Matthew.
> 
>