Re: [PATCH] hw/core/machine-smp: Remove deprecated "parameter=0" SMP configurations
Hello Zhao,
On Mon, 4 Mar 2024 at 12:19, Zhao Liu <zhao1.liu(a)linux.intel.com> wrote:
> unsigned maxcpus = config->has_maxcpus ? config->maxcpus :
0;
This indicates the default maxcpus is initialized as 0 if user doesn't
specifies it.
* 'has_maxcpus' should be set only if maxcpus > 0. If maxcpus == 0,
then setting 'has_maxcpus=1' seems convoluted.
However, we could initialize maxcpus as other default value, e.g.,
maxcpus = config->has_maxcpus ? config->maxcpus : 1.
===
hw/core/machine.c
machine_initfn
/* default to mc->default_cpus */
ms->smp.cpus = mc->default_cpus;
ms->smp.max_cpus = mc->default_cpus;
static void machine_class_base_init(ObjectClass *oc, void *data)
{
MachineClass *mc = MACHINE_CLASS(oc);
mc->max_cpus = mc->max_cpus ?: 1;
mc->min_cpus = mc->min_cpus ?: 1;
mc->default_cpus = mc->default_cpus ?: 1;
}
===
* Looking at the above bits, it seems smp.cpus & smp.max_cpus are
initialised to 1 via default_cpus in MachineClass object.
> if (config->has_maxcpus && config->maxcpus == 0)
This check only wants to identify the case that user sets the 0.
If the default maxcpus is initialized as 0, then (maxcpus == 0) will
fail if user doesn't set maxcpus.
But it is still necessary to distinguish whether maxcpus is user-set or
auto-initialized.
* If it is set to zero(0) either by user or by auto-initialise, it is
still invalid, right?
If it is user-set, -smp should fail is there's invalid
maxcpus/invalid
topology.
Otherwise, if it is auto-initialized, its value should be adjusted based
on other topology components as the above calculation in (*).
* Why have such diverging ways?
* Could we simplify it as
- If cpus/maxcpus==0, it is invalid, show an error and exit.
- If cpus/maxcpus > 0, but incorrect for topology, then
re-calculate the correct value based on topology parameters. If the
re-calculated value is still incorrect or unsatisfactory, then show an
error and exit.
* Saying that user setting cpu/maxcpus=0 is invalid and
auto-initialising it to zero(0) is valid, is not consistent.
...wdyt?
---
- Prasad