Commit e5fd47bf authored Nov 21, 2011 by Konrad Rzeszutek Wilk Committed by Linus Torvalds Dec 03, 2011

xen/pm_idle: Make pm_idle be default_idle under Xen.



The idea behind commit d91ee586 ("cpuidle: replace xen access to x86
pm_idle and default_idle") was to have one call - disable_cpuidle()
which would make pm_idle not be molested by other code.  It disallows
cpuidle_idle_call to be set to pm_idle (which is excellent).

But in the select_idle_routine() and idle_setup(), the pm_idle can still
be set to either: amd_e400_idle, mwait_idle or default_idle.  This
depends on some CPU flags (MWAIT) and in AMD case on the type of CPU.

In case of mwait_idle we can hit some instances where the hypervisor
(Amazon EC2 specifically) sets the MWAIT and we get:

  Brought up 2 CPUs
  invalid opcode: 0000 [#1] SMP

  Pid: 0, comm: swapper Not tainted 3.1.0-0.rc6.git0.3.fc16.x86_64 #1
  RIP: e030:[<ffffffff81015d1d>]  [<ffffffff81015d1d>] mwait_idle+0x6f/0xb4
  ...
  Call Trace:
   [<ffffffff8100e2ed>] cpu_idle+0xae/0xe8
   [<ffffffff8149ee78>] cpu_bringup_and_idle+0xe/0x10
  RIP  [<ffffffff81015d1d>] mwait_idle+0x6f/0xb4
   RSP <ffff8801d28ddf10>

In the case of amd_e400_idle we don't get so spectacular crashes, but we
do end up making an MSR which is trapped in the hypervisor, and then
follow it up with a yield hypercall.  Meaning we end up going to
hypervisor twice instead of just once.

The previous behavior before v3.0 was that pm_idle was set to
default_idle regardless of select_idle_routine/idle_setup.

We want to do that, but only for one specific case: Xen.  This patch
does that.

Fixes RH BZ #739499 and Ubuntu #881076
Reported-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent af968e29

arch/x86/include/asm/system.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -401,6 +401,7 @@ extern unsigned long arch_align_stack(unsigned long sp);
		extern void free_init_pages(char *what, unsigned long begin, unsigned long end);

		void default_idle(void);
		bool set_pm_idle_to_default(void);

		void stop_this_cpu(void *dummy);

arch/x86/kernel/process.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -403,6 +403,14 @@ void default_idle(void)
		EXPORT_SYMBOL(default_idle);
		#endif

		bool set_pm_idle_to_default(void)
		{
		bool ret = !!pm_idle;

		pm_idle = default_idle;

		return ret;
		}
		void stop_this_cpu(void *dummy)
		{
		local_irq_disable();

arch/x86/xen/setup.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -410,6 +410,6 @@ void __init xen_arch_setup(void)
		#endif
		disable_cpuidle();
		boot_option_idle_override = IDLE_HALT;

		WARN_ON(set_pm_idle_to_default());
		fiddle_vdso();
		}

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