linux-kernel - Re: [PATCH] x86: Fix boot on uniprocessor systems

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Message-ID: <CABPqkBTk+b_+PM_YdxUYw8PDdo9PL506jCR1xzqD6=SXc+zbKg@mail.gmail.com>
Date:	Wed, 26 Mar 2014 23:01:07 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Artem Fetishev <artem_fetishev@...m.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] x86: Fix boot on uniprocessor systems

On Wed, Mar 26, 2014 at 9:31 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Tue, 25 Mar 2014 01:59:10 +0300 Artem Fetishev <artem_fetishev@...m.com> wrote:
>
>> On x86 uniprocessor systems topology_physical_package_id() returns -1 which
>> causes rapl_cpu_prepare() to leave rapl_pmu variable uninitialized which leads
>> to GPF in rapl_pmu_init(). See arch/x86/kernel/cpu/perf_event_intel_rapl.c.
>>
>> It turns out that physical_package_id and core_id can actually be retreived for
>> uniprocessor systems too. Enabling them also fixes rapl_pmu code.
>>
>> Signed-off-by: Artem Fetishev <artem_fetishev@...m.com>
>> ---
>> diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
>> index d35f24e..1306d11 100644
>> --- a/arch/x86/include/asm/topology.h
>> +++ b/arch/x86/include/asm/topology.h
>> @@ -119,9 +119,10 @@ static inline void setup_node_to_cpumask_map(void) { }
>>
>>  extern const struct cpumask *cpu_coregroup_mask(int cpu);
>>
>> -#ifdef ENABLE_TOPO_DEFINES
>>  #define topology_physical_package_id(cpu)    (cpu_data(cpu).phys_proc_id)
>>  #define topology_core_id(cpu)                        (cpu_data(cpu).cpu_core_id)
>> +
>> +#ifdef ENABLE_TOPO_DEFINES
>>  #define topology_core_cpumask(cpu)           (per_cpu(cpu_core_map, cpu))
>>  #define topology_thread_cpumask(cpu)         (per_cpu(cpu_sibling_map, cpu))
>>  #endif
>
> The patch applies to 3.13 and perhaps earlier kernels.  Is it needed in
> those kernel versions?

Before 3.13 there was no RAPL support.
But it seems the patch is still useful regardless
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