Re: [PATCH v7 09/14] arm64/numa: support HAVE_SETUP_PER_CPU_AREA

[Leizhen (ThunderTown)]

On 2016/8/26 21:28, Will Deacon wrote:
> On Wed, Aug 24, 2016 at 03:44:48PM +0800, Zhen Lei wrote:
>> To make each percpu area allocated from its local numa node. Without this
>> patch, all percpu areas will be allocated from the node which cpu0 belongs
>> to.
>>
>> Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
>> ---
>>  arch/arm64/Kconfig   |  8 ++++++++
>>  arch/arm64/mm/numa.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 63 insertions(+)
>>
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index bc3f00f..2815af6 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -603,6 +603,14 @@ config USE_PERCPU_NUMA_NODE_ID
>>  	def_bool y
>>  	depends on NUMA
>>
>> +config HAVE_SETUP_PER_CPU_AREA
>> +	def_bool y
>> +	depends on NUMA
>> +
>> +config NEED_PER_CPU_EMBED_FIRST_CHUNK
>> +	def_bool y
>> +	depends on NUMA
> 
> Why do we need this? Is it purely about using block mappings for the
> pcpu area?
Without NEED_PER_CPU_EMBED_FIRST_CHUNK, Link error will be reported.

#if defined(CONFIG_NEED_PER_CPU_EMBED_FIRST_CHUNK) || \
	!defined(CONFIG_HAVE_SETUP_PER_CPU_AREA)
#define BUILD_EMBED_FIRST_CHUNK
#endif

#if defined(BUILD_EMBED_FIRST_CHUNK)
//pcpu_embed_first_chunk definition
#endif

setup_per_cpu_areas -->pcpu_embed_first_chunk


> 
>>  source kernel/Kconfig.preempt
>>  source kernel/Kconfig.hz
>>
>> diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
>> index 7b73808..5e44ad1 100644
>> --- a/arch/arm64/mm/numa.c
>> +++ b/arch/arm64/mm/numa.c
>> @@ -26,6 +26,7 @@
>>  #include <linux/of.h>
>>
>>  #include <asm/acpi.h>
>> +#include <asm/sections.h>
>>
>>  struct pglist_data *node_data[MAX_NUMNODES] __read_mostly;
>>  EXPORT_SYMBOL(node_data);
>> @@ -131,6 +132,60 @@ void __init early_map_cpu_to_node(unsigned int cpu, int nid)
>>  	cpu_to_node_map[cpu] = nid;
>>  }
>>
>> +#ifdef CONFIG_HAVE_SETUP_PER_CPU_AREA
>> +unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
>> +EXPORT_SYMBOL(__per_cpu_offset);
>> +
>> +static int __init early_cpu_to_node(int cpu)
>> +{
>> +	return cpu_to_node_map[cpu];
>> +}
>> +
>> +static int __init pcpu_cpu_distance(unsigned int from, unsigned int to)
>> +{
>> +	if (early_cpu_to_node(from) == early_cpu_to_node(to))
>> +		return LOCAL_DISTANCE;
>> +	else
>> +		return REMOTE_DISTANCE;
>> +}
> 
> Is it too early to use __node_distance here?
Good, we can directly use node_distance, thanks.

> 
>> +static void * __init pcpu_fc_alloc(unsigned int cpu, size_t size,
>> +				       size_t align)
>> +{
>> +	int nid = early_cpu_to_node(cpu);
>> +
>> +	return  memblock_virt_alloc_try_nid(size, align,
>> +			__pa(MAX_DMA_ADDRESS), MEMBLOCK_ALLOC_ACCESSIBLE, nid);
>> +}
>> +
>> +static void __init pcpu_fc_free(void *ptr, size_t size)
>> +{
>> +	memblock_free_early(__pa(ptr), size);
>> +}
>> +
>> +void __init setup_per_cpu_areas(void)
>> +{
>> +	unsigned long delta;
>> +	unsigned int cpu;
>> +	int rc;
>> +
>> +	/*
>> +	 * Always reserve area for module percpu variables.  That's
>> +	 * what the legacy allocator did.
>> +	 */
>> +	rc = pcpu_embed_first_chunk(PERCPU_MODULE_RESERVE,
>> +				    PERCPU_DYNAMIC_RESERVE, PAGE_SIZE,
>> +				    pcpu_cpu_distance,
>> +				    pcpu_fc_alloc, pcpu_fc_free);
>> +	if (rc < 0)
>> +		panic("Failed to initialize percpu areas.");
>> +
>> +	delta = (unsigned long)pcpu_base_addr - (unsigned long)__per_cpu_start;
>> +	for_each_possible_cpu(cpu)
>> +		__per_cpu_offset[cpu] = delta + pcpu_unit_offsets[cpu];
>> +}
>> +#endif
> 
> It's a pity that this is practically identical to PowerPC. Ideally, there
> would be definitions of this initialisation gunk in the core code that
> could be reused across architectures.
But these are different from other ARCHs, except PPC.

I originally want to put it into driver/of/of_numa.c, but now the ACPI NUMA is
coming up, so I don't known where.

> 
> Will
> 
> .
>