Re: raid6 badness

[Andi Kleen <ak@suse.de>]

On Fri, 30 Jan 2004 21:50:23 -0800
"H. Peter Anvin" <hpa@zytor.com> wrote:

> Andi Kleen wrote:
> > "H. Peter Anvin" <hpa@zytor.com> writes:
> > 
> >>I don't know what would cause the stack to be misaligned, however.
> > 
> > x86-64 kernel doesn't guarantee the stack to be 16 byte aligned
> > (although it usually is). If you need 16 byte alignment you have 
> > to align yourself.
> > 
> 
> OK, that's unfortunate... per our discussion I really think this is a 
> bug, since the compiler still does 16-byte alignment, and thus we're 
> taking the cost without the benefit.

I disagree on the "bug" part. I will check with the compiler guys, but 
as long as gcc doesn't rely on 16 byte alignment I will rather just disable it 
in the compiler.

I don't see much sense in enforcing this just because of some obscure SSE2
function that can align itself. Saving instructions and stack space
would be more important.

-Andi