The following commit changes calls to pm_idle into first trying
cpuidle_call_idle() and if that returns non-zero to fall back to
call pm_idle().
commit a0bfa1373859e9d11dc92561a8667588803e42d8
Author: Len Brown <len.br...@intel.com>
Date: Fri Apr 1 19:34:59 2011 -0400
cpuidle: stop depending on pm_idle
However cpuidle_call_idle() will return -ENODEV if it is supposed to be
disabled by cpuidle.off. Which then causes pm_idle() to be called.
This has some bad interaction with the following change that tries to
make use of disabling cpuidle in Xen to fall back to hlt.
commit d91ee5863b71e8c90eaf6035bff3078a85e2e7b5
Author: Len Brown <len.br...@intel.com>
Date: Fri Apr 1 18:28:35 2011 -0400
cpuidle: replace xen access to x86 pm_idle and default_idle
The problem I see is that select_idle_routine() is called from
arch/x86/kernel/cpu/common.c and since Xen setup does not set pm_idle anymore,
it can cause mwait_idle or amd_e400_idle functions get selected.
In testing it seem amd_e400_idle in PVM domU at least does not immediately
cause problems, but mwait_idle just causes crashes. From the reports I have
this may be related to older Hypervisors (3.1 and older) not clearing the mwait
capability. But overall there seems something wrong in the interaction.
I am not really sure whether the logic of calling pm_idle() on all
errors from cpuidle_call_idle() is already flawed or the assumption in
the Xen patch about being able to prevent the wrong idle function by
turning cpuidle off is wrong.
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https://bugs.launchpad.net/bugs/881076
Title:
precise kernels do not boot on ec2
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