Re: [PATCHv8 3/5] powerpc/setup: Handle the case when boot_cpuid greater than nr_cpus

[Hari Bathini <hbathini@linux.ibm.com>]

On 09/10/23 5:00 pm, Pingfan Liu wrote:
> If the boot_cpuid is smaller than nr_cpus, it requires extra effort to
> ensure the boot_cpu is in cpu_present_mask. This can be achieved by
> reserving the last quota for the boot cpu.
> 
> Note: the restriction on nr_cpus will be lifted with more effort in the
> successive patches
> 
> Signed-off-by: Pingfan Liu <piliu@redhat.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
> Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
> Cc: Wen Xiong <wenxiong@linux.ibm.com>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Ming Lei <ming.lei@redhat.com>
> Cc: kexec@lists.infradead.org
> To: linuxppc-dev@lists.ozlabs.org
> ---
>   arch/powerpc/kernel/setup-common.c | 25 ++++++++++++++++++++++---
>   1 file changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
> index 81291e13dec0..f9ef0a2666b0 100644
> --- a/arch/powerpc/kernel/setup-common.c
> +++ b/arch/powerpc/kernel/setup-common.c
> @@ -454,8 +454,8 @@ struct interrupt_server_node {
>   void __init smp_setup_cpu_maps(void)
>   {
>   	struct device_node *dn;
> -	int shift = 0, cpu = 0;
> -	int j, nthreads = 1;
> +	int terminate, shift = 0, cpu = 0;
> +	int j, bt_thread = 0, nthreads = 1;
>   	int len;
>   	struct interrupt_server_node *intserv_node, *n;
>   	struct list_head *bt_node, head;
> @@ -518,6 +518,7 @@ void __init smp_setup_cpu_maps(void)
>   			for (j = 0 ; j < nthreads; j++) {
>   				if (be32_to_cpu(intserv[j]) == boot_cpu_hwid) {
>   					bt_node = &intserv_node->node;
> +					bt_thread = j;
>   					found_boot_cpu = true;
>   					/*
>   					 * Record the round-shift between dt
> @@ -537,11 +538,21 @@ void __init smp_setup_cpu_maps(void)
>   	/* Select the primary thread, the boot cpu's slibing, as the logic 0 */
>   	list_add_tail(&head, bt_node);
>   	pr_info("the round shift between dt seq and the cpu logic number: %d\n", shift);
> +	terminate = nr_cpu_ids;
>   	list_for_each_entry(intserv_node, &head, node) {
>   
> +		j = 0;

> +		/* Choose a start point to cover the boot cpu */
> +		if (nr_cpu_ids - 1 < bt_thread) {
> +			/*
> +			 * The processor core puts assumption on the thread id,
> +			 * not to breach the assumption.
> +			 */
> +			terminate = nr_cpu_ids - 1;

nthreads is anyway assumed to be same for all cores. So, enforcing
nr_cpu_ids to a minimum of nthreads (and multiple of nthreads) should
make the code much simpler without the need for above check and the
other complexities addressed in the subsequent patches...

Thanks
Hari

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