linux-kernel - Re: [PATCH v2 1/3] RISC-V: Add logical CPU indexing for RISC-V

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Date:   Tue, 4 Sep 2018 10:59:20 -0700
From:   Atish Patra <atish.patra@....com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     "palmer@...ive.com" <palmer@...ive.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "anup@...infault.org" <anup@...infault.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "damein@...r.kernel.org" <damein@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] RISC-V: Add logical CPU indexing for RISC-V

On 8/30/18 11:03 PM, Christoph Hellwig wrote:
> On Tue, Aug 28, 2018 at 01:36:08AM -0700, Atish Patra wrote:
>> Currently, both linux cpu id and hardware cpu id are same.
>> This is not recommended as it will lead to discontinuous cpu
>> indexing in Linux. Moreover, kdump kernel will run from CPU0
>> which would be absent if we follow existing scheme.
>>
>> Implement a logical mapping between Linux cpu id and hardware
>> cpuid to decouple these two. Always mark the boot processor as
>> cpu0 and all other cpus get the logical cpu id based on their
>> booting order.
>>
>> Signed-off-by: Atish Patra <atish.patra@....com>
>> ---
>>   arch/riscv/include/asm/smp.h | 18 +++++++++++++++++-
>>   arch/riscv/kernel/setup.c    |  2 ++
>>   arch/riscv/kernel/smp.c      | 19 +++++++++++++++++++
>>   3 files changed, 38 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/riscv/include/asm/smp.h b/arch/riscv/include/asm/smp.h
>> index 36016845..a5c257b3 100644
>> --- a/arch/riscv/include/asm/smp.h
>> +++ b/arch/riscv/include/asm/smp.h
>> @@ -22,6 +22,13 @@
>>   #include <linux/cpumask.h>
>>   #include <linux/irqreturn.h>
>>   
>> +#define INVALID_HARTID -1
>> +/*
>> + * Mapping between linux logical cpu index and hartid.
>> + */
>> +extern unsigned long __cpu_logical_map[NR_CPUS];
>> +#define cpu_logical_map(cpu)    __cpu_logical_map[cpu]
> 
> How about naming this cpuid_to_hardid_map to make things a little
> more obvious?  

Sure.
Also shouldn't this be signed given your INVALID_HARTID
> definition above.
> 

I don't know what I was thinking after adding INVALID_HARTID. I will fix 
this.

>> +static inline int riscv_hartid_to_cpuid(int hartid) { return 0 ; }
>> +static inline void riscv_cpuid_to_hartid_mask(const struct cpumask *in,
>> +				       struct cpumask *out) {
>> +	cpumask_set_cpu(cpu_logical_map(0), out);
>> +}
> 
> Please use normal coding style even for stubs:
> 
> static inline int riscv_hartid_to_cpuid(int hartid)
> {
> 	return 0;
> }
> 
> static inline void riscv_cpuid_to_hartid_mask(const struct cpumask *in,
> 			struct cpumask *out)
> {
> 	cpumask_set_cpu(cpu_logical_map(0), out);
> }
> 
>> +unsigned long __cpu_logical_map[NR_CPUS] = { [0 ... NR_CPUS-1] = INVALID_HARTID };
> 
> Please break the line into the usual format:
> 


> unsigned long __cpu_logical_map[NR_CPUS] = {
> 	[0 ... NR_CPUS-1]	= INVALID_HARTID,
> };
> 
ok.

Regards,
Atish