linux-kernel - Re: [PATCH 2/2] powerpc/topology: Check if a core is online

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Date: Tue, 25 Jun 2024 00:36:33 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: "Nysal Jan K.A." <nysal@...ux.ibm.com>
Cc: Tyrel Datwyler <tyreld@...ux.ibm.com>,
        Michal Suchanek
 <msuchanek@...e.de>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Laurent Dufour
 <ldufour@...ux.ibm.com>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, Michael Ellerman <mpe@...erman.id.au>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/2] powerpc/topology: Check if a core is online



On 6/13/24 12:20 AM, Nysal Jan K.A. wrote:
> From: "Nysal Jan K.A" <nysal@...ux.ibm.com>
> 
> topology_is_core_online() checks if the core a CPU belongs to
> is online. The core is online if at least one of the sibling
> CPUs is online. The first CPU of an online core is also online
> in the common case, so this should be fairly quick.
> 
> Signed-off-by: Nysal Jan K.A <nysal@...ux.ibm.com>
> ---
>  arch/powerpc/include/asm/topology.h | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
> index f4e6f2dd04b7..16bacfe8c7a2 100644
> --- a/arch/powerpc/include/asm/topology.h
> +++ b/arch/powerpc/include/asm/topology.h
> @@ -145,6 +145,7 @@ static inline int cpu_to_coregroup_id(int cpu)
>  
>  #ifdef CONFIG_HOTPLUG_SMT
>  #include <linux/cpu_smt.h>
> +#include <linux/cpumask.h>

Is this header file needed? 
I don't see any reference to cpumask related code. 

>  #include <asm/cputhreads.h>
>  
>  static inline bool topology_is_primary_thread(unsigned int cpu)
> @@ -156,6 +157,18 @@ static inline bool topology_smt_thread_allowed(unsigned int cpu)
>  {
>  	return cpu_thread_in_core(cpu) < cpu_smt_num_threads;
>  }
> +

This is defined only if CONFIG_HOTPLUG_SMT is true. But this could be 
generic function which might be used to check if a core is offline in other cases. 
Would that make sense to keep it out of CONFIG_HOTPLUG_SMT ?

> +#define topology_is_core_online topology_is_core_online
> +static inline bool topology_is_core_online(unsigned int cpu)
> +{
> +	int i, first_cpu = cpu_first_thread_sibling(cpu);
> +
> +	for (i = first_cpu; i < first_cpu + threads_per_core; ++i) {
> +		if (cpu_online(i))
> +			return true;
> +	}
> +	return false;
> +}
>  #endif
>  
>  #endif /* __KERNEL__ */