Re: .../asm-i386/bitops.h performance improvements

[cutaway]

The only thing I've seen so far that loses is a straight original 486.  Its
pipe is somewhat more simple minded and interlock prone than later models.
PPro, K6 and 386SX are big winners.

On the 386's, lacking actual pipeline, the compactness of the LEA over the
SHL/ADD can be more of an overriding factor.


----- Original Message ----- 
From: "Maciej W. Rozycki" <macro@xxxxxxxxxxxxxx>
To: <cutaway@xxxxxxxxxxxxx>
Cc: <linux-kernel@xxxxxxxxxxxxxxx>
Sent: Wednesday, June 15, 2005 11:34
Subject: Re: .../asm-i386/bitops.h performance improvements


>
>  Be careful about model-specific penalties from using certain address
> modes and AGIs when using "lea" for such calculations.
>
>   Maciej

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