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Concerns Over No PAE Kernel In Ubuntu 12.04 LTS

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  • Concerns Over No PAE Kernel In Ubuntu 12.04 LTS

    Phoronix: Concerns Over No PAE Kernel In Ubuntu 12.04 LTS

    One of the fundamental kernel changes that was decided upon during the Ubuntu 12.04 Developer Summit by Canonical's kernel team is to drop support for the non-PAE 32-bit Linux kernel. However, it seems there is growing resistance towards this move...

    http://www.phoronix.com/vr.php?view=MTAxMzU

  • #2
    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.

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    • #3
      Newer Ubuntu releases require instructions that older CPUs don't have (like AMD K6-2 series and older) so they won't work regardless. Nvidia drivers require SSE (fails with AMD Thunderbird for example).

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      • #4
        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.
        Yup, this is the #1 reason to not do it. Pentium M systems are still viable today, even at 6-7 years of age.

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        • #5
          People actually run default kernels? Why stress about this stuff when toggling one option and building a kernel takes less time than rebooting. Really, who cares.

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          • #6
            Nobody should be worried. It's only Ubuntu. Those that need to move probably won't miss it, as there are dozens of great alternatives.

            As pointed out, there are only a hand full of non-64bit capable machines out there that support >2GB, and even fewer of those machines actually contain >2GB. For those users of 32bit 3GB machines, they have the choice of downloading a more suitable distribution (Mint), or clicking a checkbox to enable PAE and recompiling. The down side of the latter is that it would put you into "unsupported" territory, which is fine for a technical user but bad if you have an enterprise with several hundred 32bit/3GB class Laptop PCs.

            I would like to know what server class is going to be affected. For example, will the old pre-HP "Compaq DL-380" class of server be affected (I think they were the 3000 series)? IIRC, there are quite a few 32bit 4/8GB machines doing SMB and thriving in underfunded server rooms throughout the world.

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            • #7
              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.
              Though I don't know why they did this and it seems to be another top-down decision being tossed out of the Canonical vacuum in the openwashed environment that UDS affords them, it doesn't mean that old processors that support PAE won't work.

              All it does mean is that if you have one of these old processors, you will get a kernel which can't handle more than 4 GB of RAM. Since a lot of these laptops with the aforementioned Pentium M's came with Windows XP which had no PAE abilities, and most of them had far less than 4 GB of RAM anyway, this decision won't likely affect most users even if they have a laptop with a Pentium M.

              Unlike Windows, with its arbitrary limitations, you can 1. Compile a kernel yourself with PAE support. 2. It's Ubuntu, there's probably going to be a PPA with a PAE kernel somewhere. 3. Use one for the hundreds of distributions that supports PAE if you have one of the rare 32-bit only processors that happens to support PAE, and more than 4 GB of RAM. That is an oddball combination though...

              My guess is <0.5% of Ubuntu users will even be affected by this.

              Likely, the Ubuntu kernel team came to the same conclusion and decided that maintaining an entire set of kernel packages for a handful of Ubuntu users wasn't worth it when in most cases, they can use a non-PAE kernel and not notice any difference. (But I don't think a PAE kernel will work on a non-PAE CPU, so dropping the standard 32-bit kernel for a PAE version would have affected most people still using obsolete 32-bit x86 processors.)

              Edit: But I can almost hear you screaming about Atom processors, which I like to call CPU: Starter Edition since they are extremely slow and crippled much like the Windows Starter Edition they come with. Few of them ever shipped with more than 1-2 GB of RAM since XP Starter had an arbitrary 1 GB limit where Vista7 Starter has an arbitrary 2 GB limit.
              Last edited by DaemonFC; 11-09-2011, 09:10 PM.

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              • #8
                Originally posted by DaemonFC View Post
                Edit: But I can almost hear you screaming about Atom processors, which I like to call CPU: Starter Edition since they are extremely slow and crippled much like the Windows Starter Edition they come with. Few of them ever shipped with more than 1-2 GB of RAM since XP Starter had an arbitrary 1 GB limit where Vista7 Starter has an arbitrary 2 GB limit.
                In addition: Of the few 4GB capable Atom boxes that shipped, most of them can only address 3GB

                256 --> Video memory.
                512MB --> PCI hardware resources.
                256MB --> PCI Express resources.

                Last note is for the posters that seem to think that these machines "won't run Ubuntu". This is not true, and I'm not certain where this notion came from. Ubuntu will run just fine, but will be limited to 2GB. This is more than enough RAM to boot and compile/install a PAE kernel capable of recognizing the final 1GB.

                Something tells me that owners of the "Aspire R3600" won't be interested in running Linux though.

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                • #9
                  Originally posted by russofris View Post
                  In addition: Of the few 4GB capable Atom boxes that shipped, most of them can only address 3GB

                  256 --> Video memory.
                  512MB --> PCI hardware resources.
                  256MB --> PCI Express resources.

                  Last note is for the posters that seem to think that these machines "won't run Ubuntu". This is not true, and I'm not certain where this notion came from. Ubuntu will run just fine, but will be limited to 2GB. This is more than enough RAM to boot and compile/install a PAE kernel capable of recognizing the final 1GB.

                  Something tells me that owners of the "Aspire R3600" won't be interested in running Linux though.
                  And Mary Jane Walmartshopper who bought an eMachine with her alimony. What about her? (And her cats!?)

                  They'll be heartbroken that Ubuntu doesn't support PAE, that is if they ever figure out what Ubuntu is.

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                  • #10
                    PAE kernel works fine on CPUs without PAE support, so I cannot understand what's all the fuss about.

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                    • #11
                      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?

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                      • #12
                        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.

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                        • #13
                          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.

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                          • #14
                            "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)

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                            • #15
                              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, 07:05 AM. Reason: oops

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