On 01/11/2013 08:45 AM, Jan Kiszka wrote:
> On 2013-01-11 08:37, Jan Kiszka wrote:
>>> From acc3c57390d275a1b28d66f1ec88c85e0f8c0890 Mon Sep 17 00:00:00 2001
>>> From: Gilles Chanteperdrix <[email protected]>
>>> Date: Sat, 29 Dec 2012 17:48:20 +0100
>>> Subject: [PATCH] x86/ipipe: restore warning with AMD erratum
>>>
>>> ---
>>> arch/x86/kernel/apic/apic.c | 16 ++++++++++------
>>> 1 files changed, 10 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
>>> index 7f07610..91531bb 100644
>>> --- a/arch/x86/kernel/apic/apic.c
>>> +++ b/arch/x86/kernel/apic/apic.c
>>> @@ -545,14 +545,18 @@ static void __cpuinit setup_APIC_timer(void)
>>> memcpy(levt, &lapic_clockevent, sizeof(*levt));
>>> levt->cpumask = cpumask_of(smp_processor_id());
>>> #ifdef CONFIG_IPIPE
>>> - if (!(lapic_clockevent.features & CLOCK_EVT_FEAT_DUMMY))
>>> + if (!(lapic_clockevent.features & CLOCK_EVT_FEAT_DUMMY)
>>> + && !cpu_has_amd_erratum(amd_erratum_400))
>>> levt->ipipe_timer = &__get_cpu_var(lapic_itimer);
>>> else {
>>> - printk(KERN_INFO
>>> - "I-pipe: cannot use LAPIC as a tick device\n");
>>> - if (cpu_has_amd_erratum(amd_erratum_400))
>>> - printk(KERN_INFO
>>> - "I-pipe: disable C1E power state in your BIOS\n");
>>> + static atomic_t printed = ATOMIC_INIT(-1);
>>> + printk(KERN_INFO
>>> + "I-pipe: cannot use LAPIC on cpu #%d as a tick device\n",
>>> + smp_processor_id());
>>> + if (cpu_has_amd_erratum(amd_erratum_400)
>>> + && atomic_inc_and_test(&printed))
>>> + printk(KERN_INFO
>>> + "I-pipe: disable C1E power state in your
>>> BIOS\n");
>>
>> printk_once should do the trick as well.
>
> In fact, it should actually do what you likely intended: print on first
> occurrence, not on second or later. ;)
Not quite, printk_once is not protected from the code running
concurrently on multiple cpus. So, atomic_inc_and_test is better, except
the ATOMIC_INIT needs to be set to 0.
>
> Jan
>
--
Gilles.
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