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Re: [PATCH v1 02/14] xen/riscv: introduce smp_clear_cpu_maps()


  • To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Mon, 14 Apr 2025 17:13:32 +0200
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  • Cc: Alistair Francis <alistair.francis@xxxxxxx>, Bob Eshleman <bobbyeshleman@xxxxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Mon, 14 Apr 2025 15:13:41 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 14.04.2025 17:05, Oleksii Kurochko wrote:
> On 4/10/25 3:10 PM, Jan Beulich wrote:
>> On 08.04.2025 17:57, Oleksii Kurochko wrote:
>>> +void __init smp_clear_cpu_maps(void)
>>> +{
>>> +    cpumask_clear(&cpu_possible_map);
>>> +    cpumask_clear(&cpu_online_map);
>> What's the point of these? All three maps start out fully zeroed.
> 
> It could be really dropped. I saw your patch for Arm, I'll align the current
> patch with that changes.
> 
>>> +    cpumask_set_cpu(0, &cpu_possible_map);
>>> +    cpumask_set_cpu(0, &cpu_online_map);
>> These are contradicting the name of the function. The somewhat equivalent
>> function we have on x86 is smp_prepare_boot_cpu().
>>
>>> +    cpumask_copy(&cpu_present_map, &cpu_possible_map);
>> Another cpumask_set_cpu() is probably cheaper here then.
> 
> What do you mean by cheaper here?

Less code to execute to achieve the same effect.

Jan



 


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