On Mon, Jul 25, 2016 at 11:59:21AM +0200, Igor Mammedov wrote:
> it keeps the legacy behavior for all users that doesn't care
> about stable cpu_index value, but would allow boards that
> would support device_add/device_del to set stable cpu_index
> that won't depend on order in which cpus are created/destroyed.
>
> While at that simplify cpu_get_free_index() as cpu_index
> generated by USER_ONLY and softmmu variants is the same
> since none of the users support cpu-remove so far, except
> of not yet released spapr/x86 device_add/delr, which
> will be altered by follow up patches to set stable
> cpu_index manually.
So, cpu_get_free_index() behavior is exactly the same because
cpu-remove is either unsupported, or only supported for the last
CPU. But I worry that this will easily break if anybody starts
implementing CPU removal in other machines without setting
cpu_index explicitly in the board code. Then we can make
cpu_get_free_index() generate a duplicate cpu_index.
I wonder if there any way we can add an assert() somewhere to
ensure no machine will ever allow CPU removal while not
initializing cpu_index explicitly.
(This shouldn't hold this patch, it's just a suggestion for a
possible follow-up patch).
Additional comment:
>
> Signed-off-by: Igor Mammedov <imamm...@redhat.com>
> Reviewed-by: David Gibson <da...@gibson.dropbear.id.au>
[...]
> -static int cpu_get_free_index(Error **errp)
> -{
> - int cpu = find_first_zero_bit(cpu_index_map, MAX_CPUMASK_BITS);
> -
> - if (cpu >= MAX_CPUMASK_BITS) {
> - error_setg(errp, "Trying to use more CPUs than max of %d",
> - MAX_CPUMASK_BITS);
> - return -1;
> - }
We are now relying on the rest of the QEMU code to make sure
cpu_index will be always < MAX_CPUMASK_BITS. In this case, I
suggest we add an assert() below:
[...]
> - cpu->cpu_index = cpu_get_free_index(&local_err);
> - if (local_err) {
> - error_propagate(errp, local_err);
> - cpu_list_unlock();
> - return;
> + if (cpu->cpu_index == UNASSIGNED_CPU_INDEX) {
> + cpu->cpu_index = cpu_get_free_index();
> + assert(cpu->cpu_index != UNASSIGNED_CPU_INDEX);
> }
Here:
assert(cpu->cpu_index <= MAX_CPUMASK_BITS)
Both comments can be addressed in a follow-up patch, so:
Reviewed-by: Eduardo Habkost <ehabk...@redhat.com>
--
Eduardo
