Re: [RFC][PATCH 0/5] preempt_count rework

[Peter Zijlstra]

On Wed, Aug 14, 2013 at 09:14:34AM -0700, H. Peter Anvin wrote:
> Even so, this_rq() uses __get_cpu_var() and takes its address, which
> turns into a sequence like:
> 
> 	leaq __percpu_runqueues(%rip),%rax
> 	addq %gs:this_cpu_off,%rax
> 
> ... which is better than the above but still more heavyweight than it
> would be if the pointer was itself a percpu variable.

Oh curses, this is because lea can't do segment offsets? So there's no
sane way to get addresses of per-cpu variables.

Because ideally we'd have something like:

  lea %gs:__percpu_runqueues,%rax

So in this case it makes sense to also store the actual pointer; how
unfortunate.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/