[PATCH] x86: avoid modifying global flag tsc_unstable in unsychronized_tsc()

[PATCH] x86: avoid modifying global flag tsc_unstable in unsychronized_tsc()

[Hillier, Gernot]

From: Gernot Hillier <gernot.hillier@siemens.com>

The current behavior of unsynchronized_tsc() prevents the warning for
unsychronized TSCs to be printed: tsc_init() calls unsynchronized_tsc()
first to check for such problems; if found, mark_tsc_unstable() is
called. However, the latter bails out immediately as unsynchronized_
tsc() did already set the global flag tsc_unstable. Thus, the intended
warning message "Marking TSC unstable due to TSCs unsynchronized" won't
show up.

This patch changes the behavior for unsynchronized_tsc() to only *check*
for the quirk condition, but not to modify any global flags. If I'm not
mistaken, the only place to *set* the flag shall be mark_tsc_unstable().

Signed-off-by: Gernot Hillier <gernot.hillier@siemens.com>
Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Wolfgang Mauerer <wolfgang.mauerer@siemens.com>

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index cd982f4..ffbb786 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -836,10 +836,10 @@ __cpuinit int unsynchronized_tsc(void)
 	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
 		/* assume multi socket systems are not synchronized: */
 		if (num_possible_cpus() > 1)
-			tsc_unstable = 1;
+			return 1;
 	}

-	return tsc_unstable;
+	return 0;
 }

 static void __init init_tsc_clocksource(void)

Re: [PATCH] x86: avoid modifying global flag tsc_unstable in unsychronized_tsc()

[Alok Kataria]

On Mon, 2009-10-12 at 07:22 -0700, Hillier, Gernot wrote:
> From: Gernot Hillier <gernot.hillier@siemens.com>
> 
> The current behavior of unsynchronized_tsc() prevents the warning for
> unsychronized TSCs to be printed: tsc_init() calls unsynchronized_tsc()
> first to check for such problems; if found, mark_tsc_unstable() is
> called. However, the latter bails out immediately as unsynchronized_
> tsc() did already set the global flag tsc_unstable. Thus, the intended
> warning message "Marking TSC unstable due to TSCs unsynchronized" won't
> show up.
> 
> This patch changes the behavior for unsynchronized_tsc() to only *check*
> for the quirk condition, but not to modify any global flags. If I'm not
> mistaken, the only place to *set* the flag shall be mark_tsc_unstable().

Yes, you are right. The patch looks good to me.

Thanks,
Alok

> 
> Signed-off-by: Gernot Hillier <gernot.hillier@siemens.com>
> Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
> Reviewed-by: Wolfgang Mauerer <wolfgang.mauerer@siemens.com>
> 
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index cd982f4..ffbb786 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -836,10 +836,10 @@ __cpuinit int unsynchronized_tsc(void)
>  	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
>  		/* assume multi socket systems are not synchronized: */
>  		if (num_possible_cpus() > 1)
> -			tsc_unstable = 1;
> +			return 1;
>  	}
> 
> -	return tsc_unstable;
> +	return 0;
>  }
> 
>  static void __init init_tsc_clocksource(void)
>