> Jeremy Fitzhardinge wrote:
>
>> Mike Travis wrote:
>>
>>> Ingo Molnar wrote:
>>>
>>>
>>>> * Mike Travis <travis@sgi.com> wrote:
>>>>
>>>>
>>>>
>>>>> * Declare the pda as a per cpu variable.
>>>>>
>>>>> * Make the x86_64 per cpu area start at zero.
>>>>>
>>>>> * Since the pda is now the first element of the per_cpu area,
>>>>> cpu_pda()
>>>>> is no longer needed and per_cpu() can be used instead. This
>>>>> also makes
>>>>> the _cpu_pda[] table obsolete.
>>>>>
>>>>> * Since %gs is pointing to the pda, it will then also point to the
>>>>> per cpu
>>>>> variables and can be accessed thusly:
>>>>>
>>>>> %gs:[&per_cpu_xxxx - __per_cpu_start]
>>>>>
>>>>> Based on linux-2.6.tip
>>>>>
>>>>>
>>>> -tip testing found an instantaneous reboot crash on 64-bit x86, with
>>>> this config:
>>>>
>>>>
http://redhat.com/~mingo/misc/config-Thu_Jun__5_11_43_51_CEST_2008.bad
>>>>
>>>> there is no boot log as the instantaneous reboot happens before
>>>> anything is printed to the (early-) serial console. I have bisected
>>>> it down to:
>>>>
>>>> | 7670dc09e89a2b151a1cf49eccebc07c41c2ce9f is first bad commit
>>>> | commit 7670dc09e89a2b151a1cf49eccebc07c41c2ce9f
>>>> | Author: Mike Travis <travis@sgi.com>
>>>> | Date: Tue Jun 3 17:30:21 2008 -0700
>>>> |
>>>> | x86_64: Fold pda into per cpu area
>>>>
>>>> the big problem is not just this crash, but that the patch is _way_
>>>> too big:
>>>>
>>>> arch/x86/Kconfig | 3 +
>>>> arch/x86/kernel/head64.c | 34 ++++++--------
>>>> arch/x86/kernel/irq_64.c | 36 ++++++++-------
>>>> arch/x86/kernel/setup.c | 90
>>>> ++++++++++++---------------------------
>>>> arch/x86/kernel/setup64.c | 5 --
>>>> arch/x86/kernel/smpboot.c | 51 ----------------------
>>>> arch/x86/kernel/traps_64.c | 11 +++-
>>>> arch/x86/kernel/vmlinux_64.lds.S | 1
>>>> include/asm-x86/percpu.h | 48 ++++++--------------
>>>> 9 files changed, 89 insertions(+), 190 deletions(-)
>>>>
>>>> considering the danger involved, this is just way too large, and
>>>> there's no reasonable debugging i can do in the bisection to narrow
>>>> it down any further.
>>>>
>>>> Please resubmit with the bug fixed and with a proper splitup, the
>>>> more patches you manage to create, the better. For a dangerous code
>>>> area like this, with a track record of frequent breakages in the
>>>> past, i would not mind a "one line of code changed per patch" splitup
>>>> either. (Feel free to send a git tree link for us to try as well.)
>>>>
>>>> Ingo
>>>>
>>>>
>>> Thanks for the feedback Ingo. I'll test the above config and look at
>>> splitting up the patch. The difficulty is making each patch
>>> independently
>>> compilable and testable.
>>>
>> FWIW, I'm getting past the "crashes very, very early" stage with this
>> series applied when booting under Xen. Then it crashes pretty early,
>> but that's not your fault...
>>
>> J
>>
>
> Hi Jeremy,
>
> Yes we have a simulator for Nahelem that also breezes past the boot up
> problem (actually makes it to the kernel login prompt.) Weirdly, the
> problem doesn't exist in an earlier code base so my changes are tickling
> something else newly introduced. I'm attempting to see if I can use
> GRUB 2 with the GDB stubs to track it down (which is time consuming in
> itself to setup.)
>
> It is definitely related to basing percpu variable offsets from %gs and
> (I think) interrupts.
>
