| Message ID | 20170322155906.10679-1-rkrcmar@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Mar 22, 2017 at 04:59:06PM +0100, Radim Krčmář wrote: > QEMU does not allocate based on machine's max_cpus, but only uses it to > limit the maximum selected by user and the actual limit of VCPUs is > enfoced by other components: > - machine without vIOMMU ends at 255 VCPUs > - TCG currently doesn't support x2APIC, so it also ends below 256 > - KVM with vIOMMU cannot exceed the KVM limit (currently 288) > > Using a big value should bring no drawbacks and the benefit is that > components (especially out-of-tree KVM) can bump their limits without > touching machine's max_cpus. > > max_cpus is unsigned, but it is treated as signed at least in printf and > the other two billion VCPU won't be needed for a while, so we can ignore > possible bugs by using signed max. > > Signed-off-by: Radim Krčmář <rkrcmar@redhat.com> > --- > Should the 2.9 machine type still have 288? It doesn't look like a bugfix to me. So if we can defer past 2.9 that would be best IMO. > --- > hw/i386/pc_q35.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c > index dd792a8547b3..3d5710ca20e0 100644 > --- a/hw/i386/pc_q35.c > +++ b/hw/i386/pc_q35.c > @@ -298,7 +298,7 @@ static void pc_q35_machine_options(MachineClass *m) > m->default_display = "std"; > m->no_floppy = 1; > m->has_dynamic_sysbus = true; > - m->max_cpus = 288; > + m->max_cpus = INT32_MAX; > } > > static void pc_q35_2_9_machine_options(MachineClass *m) > @@ -314,6 +314,7 @@ static void pc_q35_2_8_machine_options(MachineClass *m) > { > pc_q35_2_9_machine_options(m); > m->alias = NULL; > + m->max_cpus = 288; > SET_MACHINE_COMPAT(m, PC_COMPAT_2_8); > } > > -- > 2.12.0
2017-03-22 18:06+0200, Michael S. Tsirkin: > On Wed, Mar 22, 2017 at 04:59:06PM +0100, Radim Krčmář wrote: >> QEMU does not allocate based on machine's max_cpus, but only uses it to >> limit the maximum selected by user and the actual limit of VCPUs is >> enfoced by other components: >> - machine without vIOMMU ends at 255 VCPUs >> - TCG currently doesn't support x2APIC, so it also ends below 256 >> - KVM with vIOMMU cannot exceed the KVM limit (currently 288) >> >> Using a big value should bring no drawbacks and the benefit is that >> components (especially out-of-tree KVM) can bump their limits without >> touching machine's max_cpus. >> >> max_cpus is unsigned, but it is treated as signed at least in printf and >> the other two billion VCPU won't be needed for a while, so we can ignore >> possible bugs by using signed max. >> >> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com> >> --- >> Should the 2.9 machine type still have 288? > > It doesn't look like a bugfix to me. > So if we can defer past 2.9 that would be best IMO. Sure, I'll wait until the 2.10 machine type pops up. Thanks.
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c index dd792a8547b3..3d5710ca20e0 100644 --- a/hw/i386/pc_q35.c +++ b/hw/i386/pc_q35.c @@ -298,7 +298,7 @@ static void pc_q35_machine_options(MachineClass *m) m->default_display = "std"; m->no_floppy = 1; m->has_dynamic_sysbus = true; - m->max_cpus = 288; + m->max_cpus = INT32_MAX; } static void pc_q35_2_9_machine_options(MachineClass *m) @@ -314,6 +314,7 @@ static void pc_q35_2_8_machine_options(MachineClass *m) { pc_q35_2_9_machine_options(m); m->alias = NULL; + m->max_cpus = 288; SET_MACHINE_COMPAT(m, PC_COMPAT_2_8); }
QEMU does not allocate based on machine's max_cpus, but only uses it to limit the maximum selected by user and the actual limit of VCPUs is enfoced by other components: - machine without vIOMMU ends at 255 VCPUs - TCG currently doesn't support x2APIC, so it also ends below 256 - KVM with vIOMMU cannot exceed the KVM limit (currently 288) Using a big value should bring no drawbacks and the benefit is that components (especially out-of-tree KVM) can bump their limits without touching machine's max_cpus. max_cpus is unsigned, but it is treated as signed at least in printf and the other two billion VCPU won't be needed for a while, so we can ignore possible bugs by using signed max. Signed-off-by: Radim Krčmář <rkrcmar@redhat.com> --- Should the 2.9 machine type still have 288? --- hw/i386/pc_q35.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)