Re: Percpu data in a vsyscall page

[Rusty Russell <rusty@rustcorp.com.au>]

On Wed, 2005-11-02 at 11:54 +0100, Vojtech Pavlik wrote:
> Hi!
> 
> I'm working on a RDTSCP support on x86-64, and for that, I'll need
> per-cpu time offset table in a vsyscall page. I saw the percpu.h header,
> and thought - "Hey, I could use that!", but I think I really can't.
> 
> The data need to be in a vsyscall page, which is mapped to userspace via
> linker magic, and the percpu stuff uses a different mapping.

Yes.  The percpu stuff uses a single add to find the local value of a
variable.  This per-cpu offset can be kept in a register (I think
Sparc64 already does this) making it v. fast.

You're going to have to stick with an array I think.

Sorry,
Rusty.
-- 
A bad analogy is like a leaky screwdriver -- Richard Braakman

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