Re: [Qemu-devel] [PATCH v2 02/10] machine: introduce MachineClass.possible_cpu_arch_ids() hook

[Eduardo Habkost]

On Fri, Feb 05, 2016 at 07:06:58PM +0100, Igor Mammedov wrote:
> on x86 currently range 0..max_cpus is used to generate
> architecture-dependent CPU ID (APIC Id) for each present
> and possible CPUs. However architecture-dependent CPU IDs
> list could be sparse and code that needs to enumerate
> all IDs (ACPI) ended up doing guess work enumerating all
> possible and impossible IDs up to
>   apic_id_limit = x86_cpu_apic_id_from_index(max_cpus).
> 
> That leads to creation of MADT entries and Processor
> objects in ACPI tables for not possible CPUs.
> Fix it by allowing board specify a concrete list of
> CPU IDs accourding its own rules (which for x86 depends
> on topology). So that code that needs this list could
> request it from board instead of trying to figure out
> what IDs are correct on its own.
> 
> Signed-off-by: Igor Mammedov <address@hidden>
> ---
>  hw/i386/pc.c        | 16 ++++++++++++++++
>  include/hw/boards.h | 18 ++++++++++++++++++
>  2 files changed, 34 insertions(+)
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 9227bde..548ec64 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1931,6 +1931,21 @@ static unsigned pc_cpu_index_to_socket_id(unsigned 
> cpu_index)
>      return topo.pkg_id;
>  }
>  
> +static GArray *pc_possible_cpu_arch_ids(void)
> +{
> +    int i;
> +    GArray *list = g_array_new(FALSE, FALSE, sizeof(CPUArchId));
> +
> +    for (i = 0; i < max_cpus; i++) {
> +        CPUArchId val;
> +
> +        val.arch_id = x86_cpu_apic_id_from_index(i);
> +        val.cpu = qemu_get_cpu_by_arch_id(val.arch_id);
> +        g_array_append_val(list, val);
> +    }
> +    return list;
> +}

You claim this version is linear, but I don't see any change from
v1, except for a whitespace change.

qemu_get_cpu_by_arch_id() is O(smp_cpus). This calls
qemu_get_cpu_by_arch_id() max_cpus times, so this is
O(max_cpus*smp_cpus).

-- 
Eduardo