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Re: [Qemu-devel] [PATCH v5 1/2] vl.c deprecate incorrect CPUs topology
From: |
Igor Mammedov |
Subject: |
Re: [Qemu-devel] [PATCH v5 1/2] vl.c deprecate incorrect CPUs topology |
Date: |
Thu, 6 Sep 2018 10:02:13 +0200 |
On Wed, 5 Sep 2018 10:45:12 -0300
Eduardo Habkost <address@hidden> wrote:
> On Wed, Sep 05, 2018 at 11:25:11AM +0200, Igor Mammedov wrote:
> > On Tue, 4 Sep 2018 23:12:55 -0300
> > Eduardo Habkost <address@hidden> 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 <address@hidden>
> > > > ---
> > > > v5:
> > > > - extend deprecation doc, adding that maxcpus should be multiple of
> > > > present on CLI [sockets/cores/threads] options
> > > > (Eduardo Habkost <address@hidden>)
> > > > v4:
> > > > - missed dot comment, fix it with s/./,/ (Andrew Jones
> > > > <address@hidden>)
> > > > v3:
> > > > - more spelling fixes (Andrew Jones <address@hidden>)
> > > > - place deprecation check after (sockets * cores * threads >
> > > > max_cpus) check
> > > > (Eduardo Habkost <address@hidden>)
> > > > v2:
> > > > - spelling&&co fixes (Andrew Jones <address@hidden>)
> > > > ---
> > > > 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.
> > > >
> > > > address@hidden -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:
> > >
> > > @address@hidden <= @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:
> > >
> > > @address@hidden * @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.
I can respin if necessary (we are not in hurry so no need to merge
something that would be removed immediately).
Could you suggest a text for clarification for me to include on respin?
>
> In either case, this can be done on a follow-up patch if
> necessary.
>
> Reviewed-by: Eduardo Habkost <address@hidden>
>
- [Qemu-devel] [PATCH v5 2/2] vl:c: make sure that sockets are calculated correctly in '-smp X' case, (continued)
- [Qemu-devel] [PATCH v5 1/2] vl.c deprecate incorrect CPUs topology, Igor Mammedov, 2018/09/04
- Re: [Qemu-devel] [PATCH v5 1/2] vl.c deprecate incorrect CPUs topology, Andrew Jones, 2018/09/04
- [Qemu-devel] [PATCH v6 1/2] vl.c deprecate incorrect CPUs topology, Igor Mammedov, 2018/09/04
- Re: [Qemu-devel] [PATCH v5 1/2] vl.c deprecate incorrect CPUs topology, Eduardo Habkost, 2018/09/04
- Re: [Qemu-devel] [PATCH v5 1/2] vl.c deprecate incorrect CPUs topology, Igor Mammedov, 2018/09/05
- Re: [Qemu-devel] [PATCH v5 1/2] vl.c deprecate incorrect CPUs topology, Eduardo Habkost, 2018/09/05
- Re: [Qemu-devel] [PATCH v5 1/2] vl.c deprecate incorrect CPUs topology,
Igor Mammedov <=
- Re: [Qemu-devel] [PATCH v5 1/2] vl.c deprecate incorrect CPUs topology, Eduardo Habkost, 2018/09/10
- Re: [Qemu-devel] [libvirt] [PATCH v5 1/2] vl.c deprecate incorrect CPUs topology, Eric Blake, 2018/09/10
- Re: [Qemu-devel] [PATCH v5 1/2] vl.c deprecate incorrect CPUs topology, Igor Mammedov, 2018/09/12
Re: [Qemu-devel] [libvirt] [PATCH v5 1/2] vl.c deprecate incorrect CPUs topology, Eric Blake, 2018/09/10