Re: [PATCH v3 1/2] MIPS: CPS: Improve mips_cps_first_online_in_cluster()

["Jiaxun Yang" <jiaxun.yang@flygoat.com>]

在2025年7月8日周二 下午2:46，Gregory CLEMENT写道：
> The initial implementation of this function goes through all the CPUs
> in a cluster to determine if the current CPU is the only one
> running. This process occurs every time the function is called.
>
> However, during boot, we already perform this task, so let's take
> advantage of this opportunity to create and fill a CPU bitmask that
> can be easily and efficiently used later.
>
> This patch modifies the function to allow providing the first
> available online CPU when one already exists, which is necessary for
> delay CPU calibration optimization.
>
> Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>

Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>

Many thanks for this optimised implementation!

Thanks
- Jiaxun

> ---
>  arch/mips/include/asm/mips-cps.h |  4 +++-
>  arch/mips/include/asm/smp-cps.h  |  1 +
>  arch/mips/kernel/mips-cm.c       | 47 ++++++++++++++--------------------------
>  arch/mips/kernel/smp-cps.c       |  5 ++++-
>  4 files changed, 24 insertions(+), 33 deletions(-)
>
> diff --git a/arch/mips/include/asm/mips-cps.h 
> b/arch/mips/include/asm/mips-cps.h
> index 
> 917009b80e6951dc7e2b308ad7fb42cd9fbbf7d7..1fffd47a4564fb891d3c1e3ae3895b34d6700e5e 
> 100644
> --- a/arch/mips/include/asm/mips-cps.h
> +++ b/arch/mips/include/asm/mips-cps.h
> @@ -258,6 +258,8 @@ static inline bool mips_cps_multicluster_cpus(void)
> 
>  /**
>   * mips_cps_first_online_in_cluster() - Detect if CPU is first online 
> in cluster
> + * @first_cpu: The first other online CPU in cluster, or nr_cpu_ids if
> + * the function returns true.
>   *
>   * Determine whether the local CPU is the first to be brought online 
> in its
>   * cluster - that is, whether there are any other online CPUs in the 
> local
> @@ -265,6 +267,6 @@ static inline bool mips_cps_multicluster_cpus(void)
>   *
>   * Returns true if this CPU is first online, else false.
>   */
> -extern unsigned int mips_cps_first_online_in_cluster(void);
> +extern unsigned int mips_cps_first_online_in_cluster(int *first_cpu);
> 
>  #endif /* __MIPS_ASM_MIPS_CPS_H__ */
> diff --git a/arch/mips/include/asm/smp-cps.h 
> b/arch/mips/include/asm/smp-cps.h
> index 
> 10d3ebd890cb2f3ac2b1db5a541cfe9e7f1a0c99..88cfae5d22c83e44451200ad3daae12fced03303 
> 100644
> --- a/arch/mips/include/asm/smp-cps.h
> +++ b/arch/mips/include/asm/smp-cps.h
> @@ -24,6 +24,7 @@ struct core_boot_config {
> 
>  struct cluster_boot_config {
>  	unsigned long *core_power;
> +	struct cpumask cpumask;
>  	struct core_boot_config *core_config;
>  };
> 
> diff --git a/arch/mips/kernel/mips-cm.c b/arch/mips/kernel/mips-cm.c
> index 
> 43cb1e20baed3648ff83bb5d3bbe6a726072e063..f49138f551d3c347c6a98afe05ad5027b0d91637 
> 100644
> --- a/arch/mips/kernel/mips-cm.c
> +++ b/arch/mips/kernel/mips-cm.c
> @@ -10,6 +10,7 @@
>  #include <linux/spinlock.h>
> 
>  #include <asm/mips-cps.h>
> +#include <asm/smp-cps.h>
>  #include <asm/mipsregs.h>
> 
>  void __iomem *mips_gcr_base;
> @@ -529,39 +530,23 @@ void mips_cm_error_report(void)
>  	write_gcr_error_cause(cm_error);
>  }
> 
> -unsigned int mips_cps_first_online_in_cluster(void)
> +unsigned int mips_cps_first_online_in_cluster(int *first_cpu)
>  {
> -	unsigned int local_cl;
> -	int i;
> -
> -	local_cl = cpu_cluster(&current_cpu_data);
> +	unsigned int local_cl = cpu_cluster(&current_cpu_data);
> +	struct cpumask *local_cl_mask;
> 
>  	/*
> -	 * We rely upon knowledge that CPUs are numbered sequentially by
> -	 * cluster - ie. CPUs 0..X will be in cluster 0, CPUs X+1..Y in 
> cluster
> -	 * 1, CPUs Y+1..Z in cluster 2 etc. This means that CPUs in the same
> -	 * cluster will immediately precede or follow one another.
> -	 *
> -	 * First we scan backwards, until we find an online CPU in the cluster
> -	 * or we move on to another cluster.
> +	 * mips_cps_cluster_bootcfg is allocated in cps_prepare_cpus. If it is
> +	 * not yet done, then we are so early that only one CPU is running, so
> +	 * it is the first online CPU in the cluster.
>  	 */
> -	for (i = smp_processor_id() - 1; i >= 0; i--) {
> -		if (cpu_cluster(&cpu_data[i]) != local_cl)
> -			break;
> -		if (!cpu_online(i))
> -			continue;
> -		return false;
> -	}
> -
> -	/* Then do the same for higher numbered CPUs */
> -	for (i = smp_processor_id() + 1; i < nr_cpu_ids; i++) {
> -		if (cpu_cluster(&cpu_data[i]) != local_cl)
> -			break;
> -		if (!cpu_online(i))
> -			continue;
> -		return false;
> -	}
> -
> -	/* We found no online CPUs in the local cluster */
> -	return true;
> +	if (mips_cps_cluster_bootcfg)
> +		local_cl_mask = &mips_cps_cluster_bootcfg[local_cl].cpumask;
> +	else
> +		return true;
> +
> +	*first_cpu = cpumask_any_and_but(local_cl_mask,
> +					 cpu_online_mask,
> +					 smp_processor_id());
> +	return (*first_cpu >= nr_cpu_ids);
>  }
> diff --git a/arch/mips/kernel/smp-cps.c b/arch/mips/kernel/smp-cps.c
> index 
> 7b0e69af4097025196b93115139a5e89c1d71fcc..6c5f15293a8e58a701601b242f43ba19a6814f06 
> 100644
> --- a/arch/mips/kernel/smp-cps.c
> +++ b/arch/mips/kernel/smp-cps.c
> @@ -283,7 +283,7 @@ static void __init cps_smp_setup(void)
> 
>  static void __init cps_prepare_cpus(unsigned int max_cpus)
>  {
> -	unsigned int nclusters, ncores, core_vpes, c, cl, cca;
> +	unsigned int nclusters, ncores, core_vpes, nvpe = 0, c, cl, cca;
>  	bool cca_unsuitable, cores_limited;
>  	struct cluster_boot_config *cluster_bootcfg;
>  	struct core_boot_config *core_bootcfg;
> @@ -356,10 +356,13 @@ static void __init cps_prepare_cpus(unsigned int max_cpus)
> 
>  		/* Allocate VPE boot configuration structs */
>  		for (c = 0; c < ncores; c++) {
> +			int v;
>  			core_vpes = core_vpe_count(cl, c);
>  			core_bootcfg[c].vpe_config = kcalloc(core_vpes,
>  					sizeof(*core_bootcfg[c].vpe_config),
>  					GFP_KERNEL);
> +			for (v = 0; v < core_vpes; v++)
> +				cpumask_set_cpu(nvpe++, &mips_cps_cluster_bootcfg[cl].cpumask);
>  			if (!core_bootcfg[c].vpe_config)
>  				goto err_out;
>  		}
>
> -- 
> 2.47.2

-- 
- Jiaxun