Re: Add prefetch switch stack hook in scheduler function

[Russell King <rmk+lkml@arm.linux.org.uk>]

On Fri, Jul 29, 2005 at 10:28:26AM +0200, Ingo Molnar wrote:
> @@ -2872,10 +2878,10 @@ go_idle:
>  	/*
>  	 * Prefetch (at least) a cacheline below the current
>  	 * kernel stack (in expectation of any new task touching
> -	 * the stack at least minimally), and a cacheline above
> -	 * the stack:
> +	 * the stack at least minimally), and at least a cacheline
> +	 * above the stack:
>  	 */
> -	prefetch_range(kernel_stack(next) - MIN_KERNEL_STACK_FOOTPRINT,
> +	prefetch_range(kernel_stack(next) - L1_CACHE_BYTES,
>  		       MIN_KERNEL_STACK_FOOTPRINT + L1_CACHE_BYTES);

This needs to ensure that we don't prefetch outside the page of the
kernel stack - otherwise we risk weird problems on architectures
which support prefetching but not DMA cache coherency.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core
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