Re: [Qemu-devel] [libvirt] [PATCH v5 1/2] vl.c deprecate incorrect CPUs topology

[Eric Blake]

On 9/4/18 8:22 AM, Igor Mammedov wrote:
> -smp [cpus],sockets/cores/threads[,maxcpus] should describe topology
> so that total number of logical CPUs [sockets * cores * threads]
> would be equal to [maxcpus], however historically we didn't have
> such check in QEMU and it is possible to start VM with an invalid
> topology.
> Deprecate invalid options combination so we can make sure that
> the topology VM started with is always correct in the future.
> Users with an invalid sockets/cores/threads/maxcpus values should
> fix their CLI to make sure that
>     [sockets * cores * threads] == [maxcpus]
>
> Signed-off-by: Igor Mammedov <address@hidden>
> ---

>   
> address@hidden -smp X,[socket=a,core=b,thread=c],maxcpus=Y (since 3.1)
> +
> +CPU topology properties should describe whole machine topology including
> +possible CPUs, but historically it was possible to start QEMU with
> +an incorrect topology where
> +  sockets * cores * threads >= X && X < maxcpus
> +which could lead to an incorrect topology enumeration by the guest.
> +Support for invalid topologies will be removed, the user must ensure
> +topologies described with -smp include all possible cpus, i.e.
> +  sockets * cores * threads == maxcpus
> +Note: it's assumed that maxcpus value must be multiple of the topology
> +options present on command line to avoid creating an invalid topology.
> +If maxcpus isn't be multiple of present topology options then the condition

s/be/a/

> +(sockets * cores * threads == maxcpus) can't be satisfied and it will
> +trigger deprecation warning which later will be converted to a error.

a/a error/an error/

> +If you get deprecation warning it's recommended to explicitly specify

s/get/get a/

> +a correct topology to make warning go away and ensure that it will
> +continue working in the future.
> +
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org