On Tue, 27 Jan 2009, Tejun Heo wrote:

quoted

later). That's because they use TLB tricks for a static 64k per-cpu
area, but this doesn't scale.  That might not be vital: abandoning
that trick will mean they can't optimise read_percpu/read_percpu_var
etc as much.

Why wont it scale? this is a separate TLB entry for each processor.

Isn't something like the following possible?

#define pcpu_read(ptr)						\
({								\
	if (__builtin_constant_p(ptr) &&			\
	    ptr >= PCPU_STATIC_START && ptr < PCPU_STATIC_END)	\
		do 64k TLB trick for static pcpu;		\
	else							\
		do generic stuff;				\
})

The TLB trick is just to access the percpu data at a fixed base. I.e.
	value = SHIFT_PERCPU_PTR(percpu_var, FIXED_ADDRESS);