Re: [PATCH] x86/i386: make sure stack-protector segment base is cachealigned

[Jeremy Fitzhardinge]

On 09/03/09 14:07, Eric Dumazet wrote:
> I was referring to .data.percpu alignement requirements, not to false sharing.
>   

Yes, I know.  But the intent of DECLARE_PER_CPU_SHARED_ALIGNED is to
avoid false sharing, and so it does no alignment when CONFIG_SMP isn't
enabled.  We need alignment regardless.

> When we put a object with an align(64) requirement into a section, linker
> has to put this 2**6 alignment in resulting section.
>
> When several .o are linked together, linker has to take the biggest alignement,
> and has to put holes.
>
> Check .data.percpu size in vmlinux before and after your patch, to make sure
> it doesnt grow too much :)
>
> therefore, ____cacheline_aligned objects should be placed in
> .data.percpu.shared_aligned
>   

That section doesn't exist without SMP.  (Well,
PER_CPU_SHARED_ALIGNED_SECTION isn't defined.)

Anyway, this should sort it out.

    J