On Mon, Feb 12, 2018 at 13:42:02 +0000, Daniel Berrange wrote: > On Mon, Feb 12, 2018 at 02:31:46PM +0100, Peter Krempa wrote: > > On Mon, Feb 12, 2018 at 09:39:26 +0000, Daniel Berrange wrote: > > > On Mon, Feb 12, 2018 at 03:54:21AM -0500, Yi Wang wrote: > > > > We can't clear vcpupin settings of XML once we did vcpupin > > > > command, this is not convenient under some condition such > > > > as migration to a host with less CPUs. > > > > > > > > This patch introduces clear feature, which can clear vcpuin > > > > setting of XML using a 'c' option. > > > > > > > > Signed-off-by: Yi Wang <wang.y...@zte.com.cn> > > > > Signed-off-by: Xi Xu <xu....@zte.com.cn> > > > > --- > > > > include/libvirt/libvirt-domain.h | 11 +++++++++++ > > > > src/qemu/qemu_driver.c | 32 ++++++++++++++++++++++++-------- > > > > > > I'm not seeing a good reason for these change. There's no concept of > > > clearing > > > CPU pinning - the default is simply "pinned" to all possible CPUs, and the > > > callers should already be able to request all possile CPUs with the > > > current > > > API design. > > > > Well, the thing is that in some cases the default is not pinned to all > > pCPUs, but rather can be taken from other configuration points, e.g. > > global VM pinning bitmap. > > Which global VM pinning bitmap are you referring to ?
<vcpu placement='static' cpuset="1-4,^3,6" current="1">2</vcpu> The above 'cpuset' is the default pinning for all vcpus, unless a vcpu specifies individual other pinning. > IIRC, when we spawned QEMU we explicitly set it to use all pCPUs, so > that it doesn't inherit whatever affinity libvirtd itself has. I see > we slightly tuned that to only include CPUs that are currently online > (as reported in /sys/devices/system/cpu/online). > > Except I see it is even more complicated. We only use the online > bitmap check if virHostCPUHasBitmap() returns true. We also potentially > asked numad to give us default placement. Yes, that is the second possible source of pinning information if the user requests automatic pinning. > So as implemented this _CLEAR flag is still potentially significantly > different to what the original affinity was set to, which I think is > pretty bad semantically. I did not look at the implementation here, but basically this should do the same logic as virDomainDefGetVcpuPinInfoHelper does to determine which bitmap is actually used. The hierarchy is: 1) specific per-vcpu bitmap 2) automatic pinning from numad if enabled 3) <vcpu cpuset=''> 4) all physical vcpus present on the host. The above algorithm is used in all the pinning code to determine the effective bitmap > > > As of such the current code does not allow restoring such state since > > pinning to all pCPUs might be a desired legitimate configuration so I've > > removed the hack that deleted the pinning for such configuration a long > > time ago. This means that an explicit removal of the pinning might be a > > desired behaviour of the API, since abusing of any other value to > > restore the default state is not a good idea. > > True, but I think it rather a hack to modify this API with a flag _CLEAR > that essentially means "ignore the bitmap parameter", as opposed to > creating an API virDomainClearCPUAffinity(dom). Yes, this is probably a better solution. The API needs a 'vcpu' argument though: virDomainClearVcpuPin(virDomainPtr dom, unsigned int vcpu, unsigned int flags) > > Regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
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