Re: [PATCH 0/3] KVM-userspace: add NUMA support for guests

[Avi Kivity <avi@redhat.com>]

Daniel P. Berrange wrote:
>> The only problem is the default option for the host side, as libnuma 
>> requires to explicitly name the nodes. Maybe make the pin: part _not_ 
>> optional? I would at least want to pin the memory, one could discuss 
>> about the VCPUs...
>>     
>
> I think keeping it optional makes things more flexible for people
> invoking KVM. If omitted, then query current CPU pinning to determine
> which host NUMA nodes to allocate from. 
>   

Well, -numa itself is optional.  But yes, we could use the default cpu 
affinity mask to derive the default host numa nodes.

> The topology exposed to a guest  will likely be the same every time
> you launch a particular VM, while the guest<-> host pinning is a 
> point in time decision according to current available resources.
> Thus some apps / users may find it more convenient to have a fixed set
> of args they always use to invoke the KVM process, and instead control
> placement during the fork/exec'ing of KVM by explicitly calling 
> sched_setaffinity or using numactl to launch.  It should be easy enough
> to use sched_getaffinity to query current pining and from that determine
> appropriate NUMA nodes, if they leave out the pin=XXXX arg.
>   

I agree, nice idea.

-- 
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