linux-kernel - Re: [Xen-devel] [PATCH 1/3] cpuidle: If disable_cpuidle() is called, set pm_idle to default

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Date:	Wed, 9 Nov 2011 23:06:44 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	linux-kernel@...r.kernel.org, x86@...nel.org, len.brown@...el.com,
	tglx@...utronix.de, jeremy@...p.org, hpa@...or.com, bp@...en8.de,
	tj@...nel.org, trenn@...e.de
Cc:	stable@...nel.org, mingo@...hat.com, xen-devel@...ts.xensource.com
Subject: Re: [Xen-devel] [PATCH 1/3] cpuidle: If disable_cpuidle() is called,
 set pm_idle to default_idle.

On Tue, Nov 08, 2011 at 04:15:12PM -0500, Konrad Rzeszutek Wilk wrote:
> . however we ignore the disable_cpuidle() directive and
> in select_idle_routine() set it to type preferred by the CPU.
> 
> This is a regression introduced by
> 
>  commit a0bfa1373859e9d11dc92561a8667588803e42d8
>  Author: Len Brown <len.brown@...el.com>
>  Date:   Fri Apr 1 19:34:59 2011 -0400
> 
>      cpuidle: stop depending on pm_idle
> 
> specifically this patch:
> 
>  commit d91ee5863b71e8c90eaf6035bff3078a85e2e7b5
>  Author: Len Brown <len.brown@...el.com>
>  Date:   Fri Apr 1 18:28:35 2011 -0400
> 
>      cpuidle: replace xen access to x86 pm_idle and default_idle
> 
>      ..scribble on pm_idle and access default_idle,
>     have it simply disable_cpuidle() so acpi_idle will not load and
>     architecture default HLT will be used.
> 
> .. but the default HLT does not get used. Instead we end up in the
> situation that select_idle_routine() is called from arch/x86/kernel/cpu/common.c
> and if we called cpuidle_disable(), then the pm_idle is not set, and
> we end up setting pm_idle to mwait_idle or amd_e400_idle.
> 
> This patch uses the cpuidle_disabled() functionality and
> makes select_idle_routine() adhere to that.
> 
> Reported-by: Stefan Bader <stefan.bader@...onical.com>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>

And just found that there is a BZ for this as well:
https://bugzilla.redhat.com/show_bug.cgi?id=739499

And this patch fixes the Linux kernel to boot under Amazon EC2.

Another option which I played with today was to do this instead:

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 46d6d21..45136f2 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -448,6 +448,6 @@ void __init xen_arch_setup(void)
 #endif
        disable_cpuidle();
        boot_option_idle_override = IDLE_HALT;
-
+       pm_idle = default_idle;
        fiddle_vdso();
 }


But that defeats the whole purpose of the patch series that Len developed
where we would _not_ scribble on the pm_idle. <sigh>

Thoughts?
> 
> CC: Thomas Gleixner <tglx@...utronix.de>
> CC: Ingo Molnar <mingo@...hat.com>
> CC: "H. Peter Anvin" <hpa@...or.com>
> CC: x86@...nel.org
> CC: Len Brown <len.brown@...el.com>
> CC: Borislav Petkov <bp@...en8.de>
> CC: Tejun Heo <tj@...nel.org>
> CC: Thomas Renninger <trenn@...e.de>
> CC: stable@...nel.org
> ---
>  arch/x86/kernel/process.c |    5 +++++
>  include/linux/cpuidle.h   |    2 ++
>  2 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index e7e3b01..1f7f8c8 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -14,6 +14,7 @@
>  #include <linux/utsname.h>
>  #include <trace/events/power.h>
>  #include <linux/hw_breakpoint.h>
> +#include <linux/cpuidle.h>
>  #include <asm/cpu.h>
>  #include <asm/system.h>
>  #include <asm/apic.h>
> @@ -587,6 +588,10 @@ void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
>  	if (pm_idle)
>  		return;
>  
> +	if (cpuidle_disabled()) {
> +		pm_idle = default_idle;
> +		return;
> +	}
>  	if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) {
>  		/*
>  		 * One CPU supports mwait => All CPUs supports mwait
> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> index b51629e..123fe9e 100644
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -122,6 +122,7 @@ struct cpuidle_driver {
>  };
>  
>  #ifdef CONFIG_CPU_IDLE
> +extern int cpuidle_disabled(void);
>  extern void disable_cpuidle(void);
>  extern int cpuidle_idle_call(void);
>  
> @@ -137,6 +138,7 @@ extern int cpuidle_enable_device(struct cpuidle_device *dev);
>  extern void cpuidle_disable_device(struct cpuidle_device *dev);
>  
>  #else
> +static inline int cpuidle_disabled(void) { return 1; }
>  static inline void disable_cpuidle(void) { }
>  static inline int cpuidle_idle_call(void) { return -ENODEV; }
>  
> -- 
> 1.7.7.1
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@...ts.xensource.com
> http://lists.xensource.com/xen-devel
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