[libvirt] [PATCH] qemu: Start domain on a node without cpu affinity

[Daniel P. Berrangé]

On Wed, Aug 22, 2018 at 09:48:10AM +0200, Peter Krempa wrote:
> On Wed, Aug 22, 2018 at 00:31:29 +0300, Roman Bolshakov wrote:
> > libvirt affinity wrappers don't support macOS Thread Affinity API:
> > https://developer.apple.com/library/archive/releasenotes/Performance/RN-AffinityAPI/index.html
> > 
> > virProcessSetAffinity stub prevents libvirt from starting a qemu domain
> > on macOS:
> > 
> > $ virsh start vm
> > error: Failed to start domain vm
> > error: Process CPU affinity is not supported on this platform: Function not implemented
> > 
> > With the patch a VM can be started on macOS but some affinity-related
> > commands will return errors:
> > 
> > $ virsh vcpuinfo vm
> > error: Requested operation is not valid: cpu affinity is not supported
> > 
> > $ virsh vcpupin vm
> > VCPU: CPU Affinity
> > ----------------------------------
> >    0: 0-7
> > 
> > $ virsh vcpupin vm --live --vcpu 0 --cpulist 7
> > error: operation failed: Virt type 'qemu' does not support vCPU pinning
> > 
> > $ virsh emulatorpin vm
> > emulator: CPU Affinity
> > ----------------------------------
> >        *: 0-7
> > 
> > $ virsh emulatorpin vm --live --cpulist 7
> > error: Requested operation is not valid: cpu affinity is not supported
> > 
> > The patch also fixes virmacmaptest on macOS
> > 
> > Signed-off-by: Roman Bolshakov <r.bolshakov at yadro.com>
> > ---
> >  src/qemu/qemu_driver.c | 6 ++++++
> >  src/util/virprocess.c  | 2 +-
> >  2 files changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> > index 21e9e87ddd..2e225b1ede 100644
> > --- a/src/qemu/qemu_driver.c
> > +++ b/src/qemu/qemu_driver.c
> > @@ -5245,6 +5245,12 @@ qemuDomainPinEmulator(virDomainPtr dom,
> >      if (virDomainPinEmulatorEnsureACL(dom->conn, vm->def, flags) < 0)
> >          goto cleanup;
> >  
> > +    if (!qemuDomainHasVcpuPids(vm)) {
> > +        virReportError(VIR_ERR_OPERATION_INVALID,
> > +                       "%s", _("cpu affinity is not supported"));
> > +        goto cleanup;
> > +    }
> > +
> >      if (qemuDomainObjBeginJob(driver, vm, QEMU_JOB_MODIFY) < 0)
> >          goto cleanup;
> >  
> > diff --git a/src/util/virprocess.c b/src/util/virprocess.c
> > index 3988f5546c..7eaafd29f2 100644
> > --- a/src/util/virprocess.c
> > +++ b/src/util/virprocess.c
> > @@ -598,7 +598,7 @@ int virProcessSetAffinity(pid_t pid ATTRIBUTE_UNUSED,
> >  {
> >      virReportSystemError(ENOSYS, "%s",
> >                           _("Process CPU affinity is not supported on this platform"));
> > -    return -1;
> > +    return 0;
> 
> This is not a good idea. The caller should make sure that it does not
> call this function if we need to support such a code path.

Specifically I think you just need to turn qemuProcessInitCpuAffinity
into a no-op on macOS builds.

Of course if its possible to actually implement virProcessSetAffinity
on macOS that's an option too :-)

Regards,
Daniel
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