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

On Wed, Sep 05, 2018 at 11:25:11AM +0200, Igor Mammedov wrote: > On Tue, 4 Sep 2018 23:12:55 -0300 > Eduardo Habkost <ehabkost(a)redhat.com&gt; wrote: > > > On Tue, Sep 04, 2018 at 03:22:35PM +0200, 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 <imammedo(a)redhat.com&gt; > > > --- > > > v5: > > > - extend deprecation doc, adding that maxcpus should be multiple of > > > present on CLI [sockets/cores/threads] options > > > (Eduardo Habkost <ehabkost(a)redhat.com>) > > > v4: > > > - missed dot comment, fix it with s/./,/ (Andrew Jones <drjones(a)redhat.com>) > > > v3: > > > - more spelling fixes (Andrew Jones <drjones(a)redhat.com>) > > > - place deprecation check after (sockets * cores * threads > max_cpus) check > > > (Eduardo Habkost <ehabkost(a)redhat.com>) > > > v2: > > > - spelling&&co fixes (Andrew Jones <drjones(a)redhat.com>) > > > --- > > > qemu-deprecated.texi | 19 +++++++++++++++++++ > > > vl.c | 7 +++++++ > > > 2 files changed, 26 insertions(+) > > > > > > diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi > > > index 87212b6..827c3ce 100644 > > > --- a/qemu-deprecated.texi > > > +++ b/qemu-deprecated.texi > > > @@ -159,6 +159,25 @@ The 'file' driver for drives is no longer appropriate for character or host > > > devices and will only accept regular files (S_IFREG). The correct driver > > > for these file types is 'host_cdrom' or 'host_device' as appropriate. > > > > > > +@subsection -smp X,[socket=a,core=b,thread=c],maxcpus=Y (since 3.1) > > > > Minor: I suggest using @var markup, or maybe just use > > "-smp (invalid topologies) (since 3.1)" as subsection title for simplicity? > > > > > + > > > +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 > > > > Minor: this line formatting is lost on the HTML output. I > > suggest using @var and/or @math. > > > > Minor: I suggest not using C syntax. > > > > i.e. use something like: > > > > @math{@var{n} <= @var{sockets} * @var{cores} * @var{threads} < @var{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 > > > > Minor: same as above. I suggest: > > > > @math{@var{sockets} * @var{cores} * @var{threads} = @var{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. > > > +If you get deprecation warning it's recommended to explicitly specify > > > +a correct topology to make warning go away and ensure that it will > > > +continue working in the future. > > > > I don't understand the purpose of the "Note:" section. It seems to duplicate > > what was already said in the lines above it. Can we just remove it? > Well, didn't I say that no additional explanation needed in v4? > Note section was added per your suggestion to explicitly say that maxcpus > should be multiple of options present on CLI. You are right: I did ask for additional clarification on the documentation, because it was not clear that the warning can still appear even if some of the sockets/cores/threads options were omitted. The note didn't make that clearer to me, though.

In either case, this can be done on a follow-up patch if necessary. Reviewed-by: Eduardo Habkost <ehabkost(a)redhat.com&gt;