2009-10-12 15:01:00

by Gernot Hillier

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

From: Gernot Hillier <[email protected]>

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 <[email protected]>
Reviewed-by: Jan Kiszka <[email protected]>
Reviewed-by: Wolfgang Mauerer <[email protected]>

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)

2009-10-13 01:22:17

by Alok Kataria

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

On Mon, 2009-10-12 at 07:22 -0700, Hillier, Gernot wrote:
> From: Gernot Hillier <[email protected]>
>
> 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 <[email protected]>
> Reviewed-by: Jan Kiszka <[email protected]>
> Reviewed-by: Wolfgang Mauerer <[email protected]>
>
> 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)
>