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Thread: Why the pae kernel

  1. #111
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    Re: Why the pae kernel

    It would be awesome if someone could confirm this bug and include an effected hardware profile:

    https://bugs.launchpad.net/ubuntu/+s...ux/+bug/930447

  2. #112
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    Re: Why the pae kernel

    Quote Originally Posted by kansasnoob View Post
    No idea, but all suggestions are welcome

    Since I don't have any effected hardware I can't effectively test that but I certainly hope someone will.

    Many thanks
    If you do a virtualbox, you not only have to make sure 'PAE/NX' is not checked, but also run with VT-X disabled. Then you'll have a virtual machine with no PAE flag and you'll get the error.

  3. #113
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    Re: Why the pae kernel

    Quote Originally Posted by effenberg0x0 View Post
    (Keep in mind I'm really tired and haven't really read the entire discussion.)

    What if you add a mem=4096M kernel parameter at the kernel cmdline? Wouldn't that sort of override CONFIG_HIGHMEM64G=y and act like if CONFIG_HIGHMEM4G=y was set in the kernel config? Or then you just get a panic?
    (I don't have non-pae hw to test).

    Regards,
    Effenberg
    CONFIG_X86_PAE=y is the relevant config option so I don't think that'll make a difference.

  4. #114
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    Re: Why the pae kernel

    Quote Originally Posted by kansasnoob View Post
    <Snip>
    Adding, for the anal among us, I do NOT need non-pae but some people will need it!

    If I limited my testing to only what effects me I wouldn't really be a tester

    • LMAO.. kansas I be thinking some of those anal peeps are commentors not testers anyway you made my day THX
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  5. #115
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    Re: Why the pae kernel

    Quote Originally Posted by xyzzyman View Post
    CONFIG_X86_PAE=y is the relevant config option so I don't think that'll make a difference.
    Hey xyzzyman,

    I think I didn't express myself decently. Of course .config will do nothing if a kernel is not rebuilt. But, I was considering if no memory is used over the 4GB limit, the panic on boot could be avoided. Considering CONFIG_X86_PAE=y depends on CONFIG_HIGHMEM64G=y, if one limits ram usage to 4GB via kernel boot parameter, I wondered if it would be like when when you set CONFIG_HIGHMEM4G=y (which would invalidate CONFIG_X86_PAE=y).

    In other words, if you have a pae-kernel in non-pae hardware, but you force the kernel to stay under 4GB: is that enough to boot, or do you get a panic anyway?

    I thought it would be a good shot. But I have just tested a pae-kernel in a non-pae VM and no matter what kernel parameter I try, the "get an adequate Kernel" shows. You can't even kexec into a pae-kernel without crashing.

    Regards,
    Effenberg

  6. #116
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    Re: Why the pae kernel

    Quote Originally Posted by effenberg0x0 View Post
    Hey xyzzyman,

    I think I didn't express myself decently. Of course .config will do nothing if a kernel is not rebuilt. But, I was considering if no memory is used over the 4GB limit, the panic on boot could be avoided. Considering CONFIG_X86_PAE=y depends on CONFIG_HIGHMEM64G=y, if one limits ram usage to 4GB via kernel boot parameter, I wondered if it would be like when when you set CONFIG_HIGHMEM4G=y (which would invalidate CONFIG_X86_PAE=y).

    In other words, if you have a pae-kernel in non-pae hardware, but you force the kernel to stay under 4GB: is that enough to boot, or do you get a panic anyway?

    I thought it would be a good shot. But I have just tested a pae-kernel in a non-pae VM and no matter what kernel parameter I try, the "get an adequate Kernel" shows. You can't even kexec into a pae-kernel without crashing.

    Regards,
    Effenberg
    I've only looked through the kernel source tree about 10 minutes, but it seems that enabling PAE is akin to the type of change of moving it to Core2 instead of just x86. It's not just enabling additional support, but it actually makes a difference on everything being compiled. So it's either PAE or not, no matter what RAM is in the unit or what limits you place. The message when you try boot is hard coded in as a hard stop instead of an actual kernel panic. I've read that you used to be able to boot further with a PAE kernel on non-PAE, so I think they've added on that on purpose 'cuz it's a guaranteed crash.

  7. #117
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    Re: Why the pae kernel

    Quote Originally Posted by kansasnoob View Post
    What I've been able to find, only the following CPU's are not supported by pae:

    Intel CPUs prior to Pentium II
    400Mhz Pentium M
    VIA C3
    Geode LX

    Of course I can't be sure, but I just tried an old 335mhz PII and even it works with pae
    At last, someone with a relevant contribution to the discussion - well done.

    There is no reason that I have yet seen not to use a PAE kernel for compatible i386 systems. The only "downside" is a slightly fatter kernel with the PAE code - which won't even be used if there is less than 4GB of RAM installed.

    If the only reason to keep a non-PAE kernel around is to support the tiny number of existing systems currently in use that need it, then that is a pretty poor reason and it is no wonder it is being phased out.

    If people want to cling onto 32-bit distributions then that is their problem, some of us have been using 64-bit Ubuntu for many years now without any significant issues (especially now Adobe have got their act together with the Flash plugin). PAE is as irrelevant to us in the same way EMS became irrelevant when the 486 CPU was released.
    Regards, David.
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  8. #118
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    Re: Why the pae kernel

    I just spent a few hours chasing my own tail

    One of the problems I was having with the non-pae mini.iso was a "no network interface found" error on my preferred testing box. It typically multi-boots Win XP and at least two *ubuntu's, and strangely I was connecting to my ethernet OK using any OS I tried, but if I'd run:

    Code:
    lspci | grep Ethernet
    There simply was no terminal output whatsoever

    I must've looked in the BIOS at least 4 times before I found that "Onboard LAN device" was disabled

    How in the world that happened, or why I still had a connection at all, I'll never understand. Don't you just hate wasting time and finding the problem was the idiot between the chair and the keyboard

  9. #119
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    Thumbs down Re: Why the pae kernel

    My opinion, no pc's with non-pae and more than 3 GB memory were -ever- built so ubuntu can save some code by not even checking....

    Jerry

  10. #120
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    Re: Why the pae kernel

    Quote Originally Posted by kansasnoob View Post
    and include an effected hardware profile
    How do you do that? I tried with apport-collect but it says that I'm not the bug submitter.
    .daniel

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