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Re: [Qemu-devel] [PATCH] hw: add .min_cpus and .default_cpus fields to m
From: |
Emilio G. Cota |
Subject: |
Re: [Qemu-devel] [PATCH] hw: add .min_cpus and .default_cpus fields to machine_class |
Date: |
Fri, 3 Nov 2017 18:24:07 -0400 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Fri, Nov 03, 2017 at 21:02:33 +0100, Eduardo Habkost wrote:
> On Fri, Nov 03, 2017 at 02:56:10PM -0400, Emilio G. Cota wrote:
> > On Fri, Nov 03, 2017 at 14:47:33 -0400, Emilio G. Cota wrote:
> > > diff --git a/hw/arm/xlnx-zcu102.c b/hw/arm/xlnx-zcu102.c
> > > index e2d15a1..395d1b5 100644
> > > --- a/hw/arm/xlnx-zcu102.c
> > > +++ b/hw/arm/xlnx-zcu102.c
(snip)
> >
> > Should we update max_cpus to just NUM_APU_CPUS as well for these boards?
> > -smp 5 or 6 (NUM_APU + NUM_RPU) still gets us 4 vCPUs.
> >
> > I see there's code for RPU cpus but it seems disabled at compile-time
> > at xlnx-zynqmp.c:431:
> > DEFINE_PROP_BOOL("has_rpu", XlnxZynqMPState, has_rpu, false)
> > Or is there a run-time way to override this?
>
> Device properties can be overridden using -global, e.g.:
>
> -global driver=xlnx,,zynqmp,property=has_rpu,value=on
>
> (",," is how commas are escaped in QEMU options)
Very interesting! This raises two separate issues.
1. Using this feature breaks 55c3cee ("qom: Introduce CPUClass.tcg_initialize",
2017-10-24). For instance:
qemu-system-aarch64 -machine xlnx-zcu102 \
-global driver=xlnx,,zynqmp,property=has_rpu,value=on
This will try to initialize TCG twice. The reason is that the second
set of CPUs (the "RPUs") is of a different "object type name", which ends
up as a different CPUClass. In xlnx-zynqmp.c:
for (i = 0; i < XLNX_ZYNQMP_NUM_RPU_CPUS; i++) {
char *name;
object_initialize(&s->rpu_cpu[i], sizeof(s->rpu_cpu[i]),
"cortex-r5-" TYPE_ARM_CPU);
This hunk only runs when we use the -global override.
This other hunk always runs. It initializes the "APUs":
for (i = 0; i < XLNX_ZYNQMP_NUM_APU_CPUS; i++) {
object_initialize(&s->apu_cpu[i], sizeof(s->apu_cpu[i]),
"cortex-a53-" TYPE_ARM_CPU);
A trivial, ugly fix would be to either use the same "object name"
for both sets of CPUs or (re)introduce a static variable in
arm_translate_init.
I'd prefer to be able to set tcg_initialized field directly for
the RPU's CPUClass. Is that possible? I don't know much about
qom/object code, so any good suggestion here would be appreciated.
2. Coming back to the original problem: given that we can get
additional vCPUs, I think we need an additional flag to signal
this. Otherwise we'll have to always do "max_cpus = mc.max_cpus",
which for most machines would be a huge waste of TCG regions.
See delta below.
Thanks,
Emilio
diff --git a/include/hw/boards.h b/include/hw/boards.h
index 62f160e..8c8ce51 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -103,6 +103,7 @@ typedef struct {
/**
* MachineClass:
* @max_cpus: maximum number of CPUs supported. Default: 1
+ * @force_max_cpus: if set, force the global max_cpus to match @max_cpus
* @min_cpus: minimum number of CPUs supported. Default: 1
* @default_cpus: number of CPUs instantiated if none are specified. Default: 1
* @get_hotplug_handler: this function is called during bus-less
@@ -181,7 +182,8 @@ struct MachineClass {
no_sdcard:1,
has_dynamic_sysbus:1,
pci_allow_0_address:1,
- legacy_fw_cfg_order:1;
+ legacy_fw_cfg_order:1,
+ force_max_cpus;
int is_default;
const char *default_machine_opts;
const char *default_boot_order;
diff --git a/hw/arm/xlnx-zcu102.c b/hw/arm/xlnx-zcu102.c
index 395d1b5..e406dc3 100644
--- a/hw/arm/xlnx-zcu102.c
+++ b/hw/arm/xlnx-zcu102.c
@@ -186,6 +186,7 @@ static void xlnx_ep108_machine_class_init(ObjectClass *oc,
void *data)
mc->units_per_default_bus = 1;
mc->ignore_memory_transaction_failures = true;
mc->max_cpus = XLNX_ZYNQMP_NUM_APU_CPUS + XLNX_ZYNQMP_NUM_RPU_CPUS;
+ mc->force_max_cpus = 1;
mc->min_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
mc->default_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
}
@@ -244,6 +245,7 @@ static void xlnx_zcu102_machine_class_init(ObjectClass *oc,
void *data)
mc->units_per_default_bus = 1;
mc->ignore_memory_transaction_failures = true;
mc->max_cpus = XLNX_ZYNQMP_NUM_APU_CPUS + XLNX_ZYNQMP_NUM_RPU_CPUS;
+ mc->force_max_cpus = 1;
mc->min_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
mc->default_cpus = XLNX_ZYNQMP_NUM_APU_CPUS;
}
diff --git a/vl.c b/vl.c
index 3ca5ee8..a21183d 100644
--- a/vl.c
+++ b/vl.c
@@ -4339,6 +4339,15 @@ int main(int argc, char **argv, char **envp)
max_cpus = machine_class->default_cpus;
}
+ /*
+ * Some boards can instantiate additional CPUs, e.g. by overriding
+ * device params via -global arguments, so they enforce the value
+ * that max_cpus should take.
+ */
+ if (machine_class->force_max_cpus) {
+ max_cpus = machine_class->max_cpus;
+ }
+
/* sanity-check smp_cpus and max_cpus */
if (smp_cpus < machine_class->min_cpus) {
error_report("Invalid SMP CPUs %d. The min CPUs "