Re: [PATCH v3 4/6] xen/cpupool: Create different cpupools at boot time

[Julien Grall <julien@xxxxxxx>]

Hi Luca,

I only skimmed through the series. I have one question below:

On 18/03/2022 15:25, Luca Fancellu wrote:
> +void __init btcpupools_allocate_pools(void)
> +{
> +    unsigned int i;
> +    bool add_extra_cpupool = false;
> +
> +    /*
> +     * If there are no cpupools, the value of next_pool_id is zero, so the code
> +     * below will assign every cpu to cpupool0 as the default behavior.
> +     * When there are cpupools, the code below is assigning all the not
> +     * assigned cpu to a new pool (next_pool_id value is the last id + 1).
> +     * In the same loop we check if there is any assigned cpu that is not
> +     * online.
> +     */
> +    for ( i = 0; i < nr_cpu_ids; i++ )
> +        if ( cpumask_test_cpu(i, &cpu_online_map) )
> +        {
> +            /* Unassigned cpu gets next_pool_id pool id value */
> +            if ( pool_cpu_map[i] < 0 )
> +            {
> +                pool_cpu_map[i] = next_pool_id;
> +                add_extra_cpupool = true;
> +            }
> +            printk(XENLOG_INFO "Logical CPU %u in Pool-%u.\n", i,
> +                   pool_cpu_map[i]);
> +        }
> +        else
> +        {
> +            if ( pool_cpu_map[i] >= 0 )
> +                panic("Pool-%d contains cpu%u that is not online!\n",
> +                      pool_cpu_map[i], i);
> +        }
> +
> +    if ( add_extra_cpupool )
> +        next_pool_id++;
> +
> +    /* Create cpupools with selected schedulers */
> +    for ( i = 0; i < next_pool_id; i++ )
> +        cpupool_create_pool(i, pool_sched_map[i]);
> +
> +#ifdef CONFIG_X86
> +    /* Cpu0 must be in cpupool0 for x86 */
> +    if ( pool_cpu_map[0] != 0 )
> +        panic("Cpu0 must be in Pool-0\n");
> +#endif
Can you document why this is necessary on x86 but not on other 
architectures?
Cheers,

--
Julien Grall