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

From: Eric Blake
Subject: Re: [Qemu-devel] [libvirt] [PATCH v5 1/2] vl.c deprecate incorrect CPUs topology
Date: Mon, 10 Sep 2018 12:58:24 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0

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
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


+(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

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