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On Thursday 02 July 2009 09:06:01 Petr Baudis wrote: > On Thu, Jul 02, 2009 at 07:42:26AM -0500, Ryan Arnold wrote: > > On Thu, Jul 2, 2009 at 6:49 AM, booleandomain 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. it is > --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). assuming some aspect of the ABI changed between .29 and .30 ... every once in a while we get a kernel update without any ABI changes ;) > 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. :-) i'm not aware of any, but i too would be interested in such info. we default to 2.6.9 in Gentoo still ... i recall there being NPTL related changes between 2.6.8 and 2.6.9 which is why we bumped it. -mike
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