Re: [PATCH] Use uname not sysctl to get the kernel revision

[H. Peter Anvin]

Eric W. Biederman wrote:
> "H. Peter Anvin" <hpa@xxxxxxxxx> writes:
>
> > Jakub Jelinek wrote:
> > > On Wed, Jul 12, 2006 at 12:33:56PM -0700, Ulrich Drepper wrote:
> > > > Roland McGrath wrote:
> > > > > We could also put the uname info (modulo nodename) into the vDSO.
> > > > Or even better: real topology information.
> > > AND rather than OR would be even better.  So glibc could find kernel
> > > version, etc. and topology in the vDSO cheaply.
> > Wouldn't it make more sense for this to be in ELF tags, rather than the vdso?
> > Another alternative, I guess, would be to put a pointer in the ELF tags, which
> > may point into the vdso.
>
> Cheap and simple access to topology information would be interesting.
>
> Glibc just wants to know if our kernel is SMP so it can know if it is
> ok to busy wait for a bit waiting for a mutex.  Or if busy waiting is
> a complete loss.
>
> The practical challenge is that topology information is not fixed but
> potentially varies at runtime.
>
> Ulrich what would be interesting besides the possibility of having
> multiple cpus?

Something that might make sense to ask CPU vendors for in the future: an 
instruction that can either trap or be a noop (or better, cpu_relax) 
based on a control register.

Not that that solves any problem any time soon.

	-hpa
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