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How expensive is highmemHow expensive is highmemPosted Oct 19, 2009 4:44 UTC (Mon) by dlang (✭ supporter ✭, #313)In reply to: How expensive is highmem by kleptog Parent article: Fixing kmap_atomic()
a64bit kernel with 32 bit userspace is reasonably common.
I've seen significant (double digit percentage) benifits from going from 32 bit to 64 bit kernels, even without himem involved (probably due to the fact that in 64 bit mode the x86 cpu's have twice as many registers available to use)
when you add the benifits of eliminating himem overhead, you should relly find it a win.
several years ago there were problems with 32 bit userspace and 64 bit kernels, but at this point I have not heard of any interface compatibility problems for a year or two.
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How expensive is highmem Posted Oct 22, 2009 18:28 UTC (Thu) by jengelh (subscriber, #33263) [Link]
>a64bit kernel with 32 bit userspace is reasonably common.
[citation needed]. It is common on arches where 64-bit is considered expensive - such as sparc64. But on x86, people have obviously made sure 64-bit mode runs at least at the same effective speed because otherwise it would be harder in selling it. Plus, in precompiled distros, the 32-bit objects often do not contain SSE/SSE2 because it is not guaranteed to be available in all cases (and in fact, libvorbis/oggenc will speed up by 17% when adding -msse -mfpmath=sse on ye olde 2003ish AMD Athlon XP); on 64-bit however, SSE is always available, so naturally it comes faster compared to precompiled 32 bit objects. (IOW, Gentoo is exempt because you can add -mfpmath=sse at your leisure.)
How expensive is highmem Posted Oct 22, 2009 18:49 UTC (Thu) by dlang (✭ supporter ✭, #313) [Link]
there is a bunch of software that is not available in 64 bit mode. As a result a lot of people on x86 use a 64 bit kernel so that they can efficiently use all of their ram, but then use 32 bit userspace so that all their apps still work.
How expensive is highmem Posted Oct 23, 2009 7:36 UTC (Fri) by Cato (subscriber, #7643) [Link]
Does anyone know if a 32 bit userland with 64 bit kernel is supported in Debian or Ubuntu? Sounds like this would be a better option than a PAE kernel for some uses.
How expensive is highmem Posted Oct 23, 2009 7:53 UTC (Fri) by dlang (✭ supporter ✭, #313) [Link]
how do you define 'supported'?
32 bit userspace with a 64 bit kernel is absolutly supported by the kernel developers
I don't think either debian or ubuntu include the option to do this in their installers, but since the packages are available if you force overriding the checks you can install the 64 bit kernel on an otherwise 32 bit install (and it will even leave your old kernel available to boot from)
will you get some people who question why you are doing this when you ask on mailing lists? yes. will you get people who are doing this on their systems when you ask on mailing lists? yes (not always at the same time)
are you talking about paid support for either of these? if so you would have to ask the support orginization. if they are any good (and are charging you enough to really offer support) I would expect them to do so.
How expensive is highmem Posted Oct 23, 2009 11:52 UTC (Fri) by mjg59 (subscriber, #23239) [Link]
It's supported in the sense that anything that doesn't work is a bug, but not supported in the sense that it's basically untested. There are certainly missing ioctl translations and suchlike, and random applications may fail as a result.
How expensive is highmem Posted Oct 23, 2009 22:02 UTC (Fri) by paulj (subscriber, #341) [Link]
Now we just need distros to support 64bit/primarily-32bit kernel/userspace.
(Fedora is tantalisingly close, but yum updates don't quite work right)
How expensive is highmem Posted Oct 24, 2009 10:54 UTC (Sat) by nix (subscriber, #2304) [Link]
In practice it works well enough for normal userspace apps. It might not
work for things that do Linux-specific stuff like iptables, but if you're running a 64-bit userspace with some 32-bit apps that you can't get 64-bit equivalents for (like World of Goo ;) ) then it should just work.
The POSIX subset of what Linux can do absolutely does work in 32-bit
How expensive is highmem Posted Oct 24, 2009 20:23 UTC (Sat) by dlang (✭ supporter ✭, #313) [Link]
actually, no.
one thing I ran into is trying to get the citrix client working (yes, a binary-only app), it needs various other libraries, including X libraries. these are not part of the stuff supported by the 32 bit compatibility libraries.
I don't run many 32 bit apps, but I've run across a half dozen of them that have required that I manually download and install some 32 bit versions of packages on my 64 bit machine before they work.
however, I have been able to get every one of them to work.
How expensive is highmem Posted Oct 24, 2009 2:23 UTC (Sat) by ccurtis (guest, #49713) [Link]
I find this question so strange ... as in, why is it even a concern?
But supported or not, my Debian servers have no issues running 32-bit userland apps. 'apt-get install ia32-libs' should be all you need.
My desktop is Ubuntu, and it appears that this package is also required for flash (nonfree). Now, as for stability I can't say I have _too_ many problems, but I wouldn't attribute any I do have to 32bit-ness.
Audio on the other hand...
How expensive is highmem Posted Oct 24, 2009 2:28 UTC (Sat) by dlang (✭ supporter ✭, #313) [Link]
installing the ia32-libs package does not take care of everything (unfortunantly)
it makes most things run, but I have run across many things that require additional 32 bit packages be installed to make them work.
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