Re: sched_setaffinity usability

[Ingo Molnar <mingo@elte.hu>]

* Helge Hafting <helgehaf@aitel.hist.no> wrote:

> Let the compile create that info file.  Then handle it much like a
> module, except that it is a "module" without any code.  I.e. copy it
> to /lib/modules/<kernelversion> if installing modules, or stuff the
> file into the initrd if making an initrd. 
> 
> Now it is in a place specific to the kernel, where a library can find
> it.

this has a couple of disadvantages:

 - the kernel can pre-map the 'file' cheaper - in fact on x86 it's
   zero-cost currently. Mapping a file takes 3 syscalls and at least one
   pagefault. Since glibc needs a good portion of this info for
   absolutely every ELF binary, why not provide it in a preconstructed
   way? x86 is doing it via the VDSO. ia64 and x86-64 is doing it via a
   dso-alike mechanism.

 - obtaining the kernel version currently needs one more syscall
   [uname()].

 - the 'metadata' becomes detached from the kernel image, so it
   cannot contain 'crutial' data. Testing kernels becomes harder, etc.
   (until now i could just send a bzImage to someone to get it tested -
    now it would have to include the metadata too.)

 - it excludes non-build-time data.

	Ingo