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Thread: Concerns Over No PAE Kernel In Ubuntu 12.04 LTS

  1. #11
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    Quote Originally Posted by birdie View Post
    PAE kernel works fine on CPUs without PAE support, so I cannot understand what's all the fuss about.
    That may be true (although I'm not so sure) but there are some processor with faulty implementation of PAE. PAE has been around since Pentium Pro but I think Pentium II doesn't handle it properly.

    In any case, PAE is necessary for Execute Disable (the capability to mark data pages as non-executable) so it's a good thing to have. However, if the hardware supports amd64 I'd recommend using a 64-bit kernel on any machine with 1GB or more. The thing is that Linux maps the physical memory in the kernel area of the virtual address space. In the default 3GB/1GB split, there's room for only 960MB of memory to be mapped. The rest is temporarily mapped in some window in the kernel virtual area (ok, I don't know exactly how it works but I'm sure about the need of additional memory management and the associated overhead). With 1-2GB memory it's better to use a 2GB/2GB split but you'll have to recompile your kernel for that. So it's better to move to 64-bit and save yourself the trouble. The memory consumption is a bit higher (I've seen quotes for about 20%) but you get generally higher performance due to the additional registers in 64-bit mode. Plus, you should be able to run a 32-bit distribution on a 64-bit kernel. I routinely do that in 32-bit root jail or LXC container.

    Has anybody tried to install a 32-bit distribution and replace the kernel with a 64-bit one to see if it works out of the box?

  2. #12
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    Default PAE kernels do not run on non-PAE machines.

    PAE kernels do not run on non-PAE machines. Been bitten by this before. This is stated clearly in the article.

    I found the comment "time to upgrade" in the article frankly offensive. We live in a world were disposable commodities and built in obsolescence cause pollution and impoverishment all over the world.

    Ubuntu, the most popular system for open source thin client systems (LTSP). We have plenty of laptops which will now not work with the next version of Ubuntu which we run as thin clients. The Pentium M is a good mobile processor and completely suitable for a number of modern workloads. There are Pentium M desktops out there too.

    Think of the impact of this on third world computing in the global south, were hardware more recent than 8 years old is "new". Ubuntu will really be stabbing Africa in the back with this move. It's not "time to upgrade" until most people have stopped using the hardware. Please don't obsolete a huge wedge of global computing resource.

    Really glad I stuck with Debian on my systems.

  3. #13
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    The only processor we really need to worry about is the Pentium M (Banias) produced between 2003 and 2005. The Pentium M (Dothan) which replaced the Banias from 2004 on supports PAE and NX bit. I know someone having two laptops with the Banias version, I may try the PAE kernel on them.

  4. #14
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    "drop support for the non-PAE 32-bit Linux kernel"

    im somehow getting the impression that either i or others understand this wrong.

    Isnt it about dropping support for Non-PAE-Kernels? which means, that if you are running a pentium M it probably wont work, as the hardware doesnt support that feature? maybe it would work, but as far as i remember the PAE kernel wasnt performing very well...

    maybe a poll to find out how many people using 32bit systems actually have more than 3,4 GB Ram, which i recall to be the physical limit of adresses on 32 bit, would be in order... calling 5-6 years outdated is ridiculous, as this is about the time span, that linux needs to support new hardware properly. seems that some people tend to forget about it.
    Also dropping the non-pae-kernel would force everyone with lower ram to use the badly performing pae kernel, which i hardly find convenient.

    Besides, id somehow suspect it to be some kind of step towards much more bloated ubuntu releases in the future... (see 750MB iso)
    sounds to me like "größenwahn" (another german word for you, michael)

  5. #15
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    Really though, who cares? That same Pentium M machine can't do a respectable job of running Windows7/8, OSX, AS400 or anything else, why not just keep Ubuntu 10.04 on there until it finally stops working? I'd rather them devote the resources to making current hardware run correctly.
    Last edited by leeenux; 11-10-2011 at 07:05 AM. Reason: oops

  6. #16
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    uh, ok... i just checked the performance concern.
    there seems to be no penalty for using PAE Kernel, as far as the last benchmarks for PAE kernels were concerned. i just hope it does apply for my system aswell...

  7. #17
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    Quote Originally Posted by rapsure View Post
    Well that mean that a lot of Pentium M laptops will not work with Ubuntu too. I tried to use PAE on all of the i686 instruction set computers and that didn't workout. Turns out that several generations of the Pentium M does not support PAE at all.
    Pentium M does not support PAE because they are not 64 bit CPUs. In fact both Pentium M (I had a Dothan as my first laptop CPU) are 32 bit as the next iteration (Pentium Core or "Core1") do not support 64 bit or PAE.

  8. #18
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    Quote Originally Posted by ciplogic View Post
    Pentium M does not support PAE because they are not 64 bit CPUs. In fact both Pentium M (I had a Dothan as my first laptop CPU) are 32 bit as the next iteration (Pentium Core or "Core1") do not support 64 bit or PAE.
    PAE has nothing to do with 64bit support. PAE has been around from before AMD64 was ever conceived.

  9. #19
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    Quote Originally Posted by ciplogic View Post
    Pentium M does not support PAE because they are not 64 bit CPUs. In fact both Pentium M (I had a Dothan as my first laptop CPU) are 32 bit as the next iteration (Pentium Core or "Core1") do not support 64 bit or PAE.
    If that were the case, then they would be advocating dropping ALL support for 32bit altogether, and forcing 64bit down everyone's throat. As it happens, I have a 32bit intel tablet that does support PAE, so THAT incorrect assumption of yours would force me right out of ubuntu altogether (assuming that I used it, which I don't...)

    Note that this dropping support for older hardware does happen over time. First the major distros dropped support for i386 (i.e. 80386 chips rather than the use as a general way of saying "32bit"), then i486, then i586 (I actually had an interesting glitch with this... apparently K6's -- including II and III -- are missing a couple of features that are required for "full" compatibility with i686, so an i686 kernel won't run on them), now its time to drop non-PAE. IMO, it is a natural and necessary progression.

    Fortunately, there isn't much risk of 32bit PAE being dropped any time soon, since this hardware is still being manufactured and advanced.

  10. #20
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    Quote Originally Posted by jakubo View Post
    "drop support for the non-PAE 32-bit Linux kernel"

    im somehow getting the impression that either i or others understand this wrong.

    Isnt it about dropping support for Non-PAE-Kernels?
    Yes; the article title is incorrect.

    which means, that if you are running a pentium M it probably wont work, as the hardware doesnt support that feature?
    Yes.

    maybe it would work, but as far as i remember the PAE kernel wasnt performing very well...
    Trying to boot a PAE kernel on hardware that doesn't support PAE leads to an instant kernel panic. Been there, done that.

    maybe a poll to find out how many people using 32bit systems actually have more than 3,4 GB Ram, which i recall to be the physical limit of adresses on 32 bit, would be in order...
    The amount of RAM installed doesn't matter. If the CPU doesn't support PAE, you can't use a PAE kernel no matter what amount of memory is installed.

    As an aside, the I suspect the real reason for Ubuntu wanting to get rid of the non-PAE kernel is that PAE kernels support NX, which is nice for improved security (you can emulate it, but that has downsides).

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