Re: FOR REVIEW: New x86-64 vsyscall vgetcpu()

[Zoltan Menyhart <Zoltan.Menyhart@bull.net>]

Andi Kleen wrote:

> That is not how user space TLS works. It usually has a base a register.

Can you please give me a real life (simplified) example?

> This means it cannot be cache colored (because you would need a static
> offset) and you couldn't share task_structs on a page.

I do not see the problem. Can you explain please?
E.g. the scheduler pulls a task instead of the current one. The CPU
will see "current->thread_info.cpu"-s of all the tasks at the same
offset anyway.

> Also you would make task_struct part of the userland ABI which
> seems like a very very bad idea to me. It means we couldn't change
> it anymore.

We can make some wrapper, e.g.:

	user_per_cpu_var(name, offset)

"vgetcpu()" would also be added to the ABI which we couldn't change
easily either.

Thanks,

Zoltan