On Wed, Oct 23, 2002 at 04:25:21PM +0000, Charles M. Hannum wrote:
> 
> Basically, I mean the following patch, although I haven't tested it
> yet:

>  	movzbl	P_PRIORITY(%eax),%edx
> -	shrl	$2,%edx
> -	btsl	%edx,_C_LABEL(sched_whichqs)	# set q full bit
> -	leal	_C_LABEL(sched_qs)(,%edx,8),%edx # locate q hdr
> +	andl	$-4,%edx
> +	movl	powerof2(%edx),%ecx
> +	orl	%ecx,_C_LABEL(sched_whichqs)	# set q full bit
> +	leal	_C_LABEL(sched_qs)(%edx,%edx),%edx # locate q hdr

It has to be faster to do:
	movzbl	P_PRIORITY(%eax),%cl
	shrb	$1,%cl
	shrb	$1,%cl
	movl	$1,%edx
	shrl	%cl,%edx
	orl	%edx,_C_LABEL(sched_whichqs)
	leal	_C_LABEL(sched_qs)(,%ecx,8),%ecx
Although that is a rather long chain of dependant instructions.

I can't believe that your lookup table will actually be in the cache.

	David

-- 
David Laight: david@l8s.co.uk