Re: pthread_create() slow for many threads; also time to revisit 64b context switch optimization?

[Jamie Lokier <jamie@shareable.org>]

Ingo Molnar wrote:
> As unimplemented flags just get ignored by the kernel, if this flag goes 
> into v2.6.27 as-is and is ignored by the kernel (i.e. we just use a 
> plain old 64-bit [47-bit] allocation), then you could do the glibc 
> change straight away, correct? So then if people complain we can fix it 
> in the kernel purely.
> 
> how about this then?

> +#define MAP_64BIT_STACK 0x20000         /* give out 32bit addresses on old CPUs */

I think the flag makes sense but it's name is confusing - 64BIT for a
flag which means "maybe request 32-bit stack"!  Suggest:

+#define MAP_STACK       0x20000         /* 31bit or 64bit address for stack, */
+                                        /* whichever is faster on this CPU */

Also, is this _only_ useful for thread stacks, or are there other
memory allocations where 31-bitness affects execution speed on old P4s?

-- Jamie

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