Kernel Optimizations Regarding SSE

Kris Kennaway kris at obsecurity.org
Sun May 29 11:29:44 PDT 2005


On Sun, May 29, 2005 at 10:48:20AM -0400, Anthony M. Agelastos wrote:
> Hello all,
> 
> I am, as we converse, rebuilding world to 5-STABLE (from 5.4-STABLE 3  
> weeks ago). This is the first time that I am building a custom kernel  
> and it only deviates from GENERIC in that I only have
> 
> cpu         I686_CPU (without the I586 and I486 that were there from  
> GENERIC)
> 
> and I added
> 
> option    CPU_ENABLE_SSE (per the Handbook's suggestion for Video  
> Playback)
> 
> That is it. In watching the compile of the new kernel, I notice that  
> just about every cc command has the options:
> 
> -mno-mmx -mno-3dnow -mno-sse -mno-sse2
> 
> Is it me, or does those flags appear to be turning off the very thing  
> I wanted turned on (to turn it on, wouldn't it be -mmmx -m3dnow -msse  
> -msse2)?

You misunderstand what the option does.  It allows user code to use
SSE, it doesn't cause SSE to be magically used in the kernel.  Indeed,
this is not feasible; please search the mailing list archives for
extensive discussion of this issue.

Kris

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