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Re: Linux kernel headers


On Thu, Jul 02, 2009 at 07:42:26AM -0500, Ryan Arnold wrote:
> On Thu, Jul 2, 2009 at 6:49 AM, booleandomain<booleandomain@gmail.com> wrote:
> > Third: can I specify --enable-kernel=2.6.30 even if my host os run version
> > 2.6.29? or should I stick to 2.6?
> 
> Using plain old 2.6 is way too old.
> 
> You _may_ be able to get away with 2.6.30.  We try to make sure that
> GLIBC doesn't use version specific facilities without asking the
> kernel if they're available but you can't always query for every
> feature.  It is guaranteed that if you specify 2.6.20 you won't get
> any facilities provided by 2.6.29.  If you specify 2.6.30 your running
> GLIBC may try to determine if the kernel on the system is really a
> 2.6.30 system before using a 2.6.29 facilitiy.

Actually, it's the other way around I think.

--enable-kernel is the _minimal_ version glibc supports. It means that
it assumes that features present in this kernel version are present and
it does not waste cycles checking their presence and having
compatibility code compiled in. So, if you specify 2.6.30, your glibc
may not work with 2.6.29, but if you specify 2.6.29, your glibc will
certainly work with 2.6.30 (albeit slightly less efficiently in theory).

I actually plan to do some benchmarks on how various settings affect
this since for historical reasons, in SUSE we still use
--enable-kernel=2.6.4. If you know about any existing benchmarks,
I would appreciate that. :-)

-- 
				Petr "Pasky" Baudis
The lyf so short, the craft so long to lerne. -- Chaucer


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